"Additionally my client then tied the same amounts to her bank account to confirm the deposits matched the amounts shown on the website.  The amounts are rock solid."

Did you pull the tax account transcript for these people? What you see there is what the IRS issued. The IRS is not using your clients' Banking records.

I don't know if all of this helps, but I would point out there is not much use in reiterating the same statements over and over. What has been provided should be enough for you to what you first ask: Understand the payments, understand the qualification, put the two together, and do the due diligence for your clients as compared to the IRS info.

"The client owes the difference." Clients?

Just to further clarify: you stated the taxpayer owed for the 1040. That means the RRC on the form as filed is over-credited, and with the adjustment, there is more tax owed after all.

It isn't the RRC that is owed. It is the lack of more RRC that results in a tax payment needing to be made.

I also thank @rbynaker for doing that math. I will now close the Excel window I left open  🙂