"I have self employed who didn't get enough RRC, some that received too much RRC and the correct amount of RRC and also straight up W-2 clients with the RRC being correct, over and under. The one W-2 client told me today his was off by $161.13 and has worked for the same major corporation for many years, so I know we didn't miss anything."

RRC is not related to employment. Perhaps you are confusing this with ERC? Dang acronyms.

The self-employed person who attempts to defer SE but has enough paid in (through estimates or whatever) will not be refunded the deferred SE. That's about the only way employment relates to RRC.

"His first RRC was short,"

Because the amount was only a projection.

"so I suspect the IRS adjusted it further,"

The 2020 tax form is based on actual credit qualified for, against the prepayment. It isn't further adjusted. It is what it is, computed.

"but why isn't ProSeries picking this up?"

Have you confirmed that what they already got is what they told you and what you entered?

Did you have them get their Tax Account Transcript?

"I suspect these clients are getting paid interest since the amount include some change so I can't tell exactly the amount of the difference and the interest."

That's going to be listed in the transcript.

"and it was very general about the change and we still don't know. He is well below the limits for his RRC to have been adjusted."

The transcript is the place to start. You and the taxpayer can both know.