Data fidelity: How to prove accuracy before filing

Your vendor promises your data transferred correctly. Your clients need proof.

There’s a gap between what migration software claims and what you can actually verify. Vendors will tell you their conversion process is reliable, their algorithms are tested, their track record speaks for itself. And maybe that’s all true. But when a client asks whether their depreciation schedule spanning fifteen years made it through intact, “the vendor said it would” isn’t the answer that builds confidence.

Here’s what separates firms that transition smoothly from firms that spend busy season firefighting data issues: proof. Not reassurance. Not vendor guarantees. Documented evidence that every client record, every carryforward calculation, every prior-year data point survived migration exactly as it should have.

The firms that enter peak season with calm control aren’t the ones who trusted the process. They’re the ones who verified it. They ran parallel operations before peak season, compared outputs side by side, flagged discrepancies while there was still time to fix them, and built documentation that proves accuracy rather than assuming it.

If you’re mid-migration or considering a switch, pre-peak season is when you turn vendor promises into verified proof. Here’s how firms actually test data fidelity before the busy season removes their flexibility to catch problems.

Why “trust us” isn’t good enough

The conversation happens before every busy season. A long-time client calls. They’ve heard you’re switching systems. Their question: “Will my information transfer correctly?”

You can offer vendor reassurances. The migration process is reliable. Thousands of firms have switched successfully. But that’s not what they’re actually asking. They want to know whether their estimated payments, depreciation schedules, and state tax credits are intact. They’re asking about their specific data.

And you won’t know the answer unless you’ve actually checked.

The 3-layer verification approach

Data fidelity isn’t a single check. It’s three distinct validation layers that prove different aspects of your migration actually worked.

Carryforward data integrity

Start with the data that spans multiple years. Prior-year returns, depreciation schedules, state apportionment history, and estimated payment records. This is the information that compounds across tax seasons, and gaps here create problems that ripple forward.

Pull sample returns from last season representing your typical complexity mix. Compare carry-forward values side by side between old and new systems. Check whether depreciation schedules continued without interruption, whether state credits carried forward correctly, and whether estimated payments for quarterly filers are intact. Most firms find that standard carryforwards transfer cleanly. The exceptions, like custom entries, unusual depreciation methods, and firm-specific calculations, get flagged now while there’s time to investigate.

Calculation accuracy

Carry-forward data is half the equation. The other half is whether your new system processes that data correctly.

Process your test returns completely through the new platform. Compare outputs with prior-year results. Validate that federal calculations match, state taxes compute correctly, credits and deductions flow through as expected. Pay particular attention to complex scenarios: multi-state returns, partnership K-1s, alternative minimum tax calculations.

You’re looking for calculation consistency, not perfection. If a return processed through both systems produces identical results, your migration succeeded. If outputs differ, you’ve found something that needs resolution before you’re processing live client work. Tools like ProConnect include comparison reports that show calculation differences automatically, so you’re not manually checking every line item.

Success looks like the vast majority of standard returns matching perfectly. The remaining edge cases, usually unusual situations or state-specific quirks, get documented and resolved during pre-peak season when you’ve got support bandwidth to work through issues methodically.

Audit trail completeness

Data and calculations matter for tax accuracy. Audit trails matter for compliance and client confidence.

Verify that your new system tracks who accessed what and when. Confirm that change logs show modifications and approvals. Check that e-signature trails are complete and compliance documentation is intact. This isn’t just regulatory housekeeping. When clients ask questions about their returns, when partners need to review decisions made months ago, when auditors want to see your process, complete audit trails are what turn “we think this is right” into “here’s documented proof.”

Test whether your audit trail captures the level of detail you need. Process a few returns through your complete workflow, preparation, review, approval, e-file, and verify that every step is documented. If gaps exist in your tracking, you’ll discover them now rather than when someone asks for documentation you assumed existed.

What verification actually looks like in practice

Here’s what one firm with about 400 clients actually did during their pre-peak season parallel run.

They selected 25 returns representing their typical work mix. Five straightforward W-2 returns. Eight Schedule C filers with varying complexity. Four partnership returns with K-1s. Three multi-state scenarios. Five returns with rental properties and depreciation schedules spanning years. They weren’t trying to test everything. They were testing whether their representative client base transferred correctly.

The process took about six hours spread across two weeks. Not six hours of someone’s dedicated time, but six hours total of running returns, comparing outputs, documenting results. A senior preparer handled most of it. A reviewer spot-checked the comparisons. A partner signed off on the findings.

What they discovered: 23 of 25 returns matched perfectly between old and new systems. Carry-forward amounts aligned. Calculations produced identical results. State apportionments computed correctly. For those 23 returns, verification was simple – compare, confirm match, document success, move on.

Two returns flagged discrepancies. One client had a custom depreciation schedule using a method that didn’t map automatically during migration. Another had a state tax credit that required manual entry in the old system, and that manual entry didn’t transfer. Neither issue was complex or unfixable. Both required about thirty minutes of work with support to resolve and retest.

Here’s what made the difference: they found those issues before busy season, when discovery meant “let’s fix this now” rather than in busy season when discovery would have meant “why is this client’s return wrong and what else did we miss?”

Their migration log was straightforward. A spreadsheet tracking client name, return type, test date, match result, any discrepancies found, resolution notes, and reviewer sign-off. Nothing elaborate. Just documentation showing they’d tested systematically and verified accuracy before committing fully to the new system.

When their managing partner asked whether they were confident in the migration, they didn’t offer reassurances. They showed him the log. When clients asked whether their data transferred correctly, they referenced the testing process and showed comparison outputs for anyone who wanted to see specifics.

By the time they shifted from parallel operations to full production, they weren’t hoping the migration worked. They had documentation proving it did.

The documentation that builds confidence

The testing matters. The documentation is what makes testing valuable beyond the moment.

When you verify data fidelity before busy season, you’re creating evidence that proves migration worked. That evidence serves multiple purposes, most of them showing up later when you need credibility fast.

What to document: Track which returns you tested and why. Note comparison results, such as what matched, what flagged discrepancies. Record how you resolved issues. Get reviewer sign-off. Keep a simple timeline.

A spreadsheet works. Client file, return type, test date, results (match/discrepancy), resolution notes, reviewer initials. You’re creating a trail that shows systematic testing, not hoping for comprehensive documentation awards.

Why this matters: Client communication is obvious. When someone asks whether their data transferred correctly, you’re showing the testing process and comparison results. Evidence, not reassurance.

But it goes beyond clients. Partners need confidence before final cutover? Present test results. Internal audit asks about migration validation? Show your verification process. Regulatory questions about data handling? Demonstrate systematic testing.

Mid-busy season, when pressure is high and someone questions whether a return is correct, you’re not second-guessing your migration. You’re referencing pre-peak testing that proved accuracy before volume hit.

Pre-busy season testing takes hours. Documentation takes minutes. That combination transforms “we think this worked” into “here’s proof it did.” And that shift from assumption to certainty lets you enter busy season with confidence instead of hope.

What firms discover during testing

Here’s what verification consistently reveals: most of your data transferred perfectly, and the parts that didn’t are fixable when you catch them early.

The pattern firms see during parallel runs is remarkably consistent. Standard returns, like straightforward W-2s, typical Schedule Cs, and common deductions, match reliably and predictably. Federal calculations align. State taxes compute correctly. Carryforward amounts populate as expected. For the bulk of your client base, verification confirms that migration worked exactly as it should have.

The remaining edge cases need attention, but they’re rarely catastrophic. Custom entries that don’t map automatically. Firm-specific workflows that require reconfiguration. State-specific calculations that need manual adjustment. Unusual depreciation methods. Tax credits that were manually entered in your old system and didn’t transfer with the automated data.

None of these issues are unfixable. All of them are manageable when discovered during pre-peak season testing. What makes them problematic is discovering them mid-busy season when you’re processing live client work under deadline pressure.

One firm found three clients with custom depreciation schedules that didn’t map during migration. Resolution took about two hours total working with support. Another discovered state apportionment rules for one jurisdiction needed manual configuration. Fixed in an afternoon. A third flagged estimated payment records for quarterly filers that required verification. Resolved before they processed a single current-year return.

The firms that complete year-end verification don’t report finding zero issues. They report finding small, expected issues that got resolved before consequences mattered. That’s the point. Testing reveals what needs attention while you still have bandwidth to address it properly.

By the time your busy season arrives, you’re not wondering whether your migration worked. You’ve already proven it did, documented the results, and resolved anything that needed fixing. That’s the foundation of migration confidence.

From testing to certainty

The firms that enter peak season confidently aren’t the ones who trusted vendor promises about data accuracy. They’re the ones who verified those promises before busy season when testing was still possible.

Your parallel run proves what transferred correctly, reveals what needs attention, and creates documentation that turns assumptions into evidence. That process takes hours during the validation window. Skipping it means discovering data issues during the busy season when resolution happens under pressure and clients are waiting.

By the time you finish verification, you’ll know whether your migration succeeded. Your data reconciliation is documented. Your calculations are validated. Your audit trails are intact. You’ve got proof, not hope.

The time investment is real, six to eight hours spread across a few weeks. But that investment buys something valuable: certainty. And certainty is what lets you cut over from parallel operations to full production knowing your systems work, your data is intact, and your clients’ information survived migration exactly as it should have.

Prove it now. Control the busy season later.

Frequently asked questions

How many returns should I test to feel confident?

Start with 20 to 30 returns representing your typical complexity mix. Include straightforward returns, complex scenarios, multi-state situations, partnership K-1s, whatever reflects your actual client base. You’re not trying to test every possible edge case. You’re validating that your representative work transfers correctly. If your first batch shows that the vast majority match correctly, you’ve likely proven what you need to know. If you’re seeing widespread issues, expand testing until you understand the pattern.

What if I find calculation differences during testing?

Small discrepancies on custom entries or firm-specific workflows are normal and fixable. Document what you find, work with support to resolve it, then retest those specific scenarios to confirm the fix worked. If you’re seeing major calculation errors or widespread data issues across multiple returns, that’s a signal to pause and investigate before committing fully. Better to discover that during pre-peak season testing when you have options than mid-busy season when you’re locked in.

Do I need to test every client’s return or just a sample?

Sample-based verification is standard practice. You’re proving your migration process worked, not individually verifying every client file. A representative sample of 20 to 30 returns gives you confidence that the conversion handled your typical work correctly. If specific clients have unusual situations like decades of depreciation schedules, complex multi-state scenarios, custom calculations, consider testing those individually. But for your standard client base, systematic sampling is sufficient to build confidence.