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@AnmarieA wrote:

My approach to this client is to prepare his 2022 return, file and then work backwards for years 2015-2021 as he pulls his information together.

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Shouldn't you start with the oldest year first?  There could be things that affect future years, such as carryovers, depreciation and perhaps other things.  You would also want to first try to get the 2014 and older years to see if anything needs to be carried over to 2015.

Usually the IRS only wants/enforces the last six years of tax returns, so maybe you could skip the oldest year or two. 

https://www.irs.gov/irm/part4/irm_04-012-001#idm139937440926592

For multi-late year filers like this, ALWAYS get paid in advance or on a retainer.  Don't do any work until you are paid.