Thanks for the detailed answer.

> It is the former employees for up to 15 years that make the contacting step difficult. They all need to provide bank/tax details.

Give people 30 dollars extra on their way out, and only contact them when you used up that budget? (Should take care of the majority of cases?)

> Edit: I should have said, I did see companies rounding all amounts up to some small amount, like $1, so your suggestion is good. It just doesn't save effort on recalculation, or much effort in getting people to dig the email out of their trash folder and provide their information to receive their $1.

Oh, my suggestion was to do the calculation, as arduously as you describe, compare with what you already overpaid earlier voluntarily, and if the company is still in the green, then don't bother contacting anyone.

Or is that not possible?

I think when companies found out that they had an issue with their Payroll software calculations, they mostly tried to solve it as quickly as possible, to put a line in the sand - from that point onwards at least, no additional errors were being made. But they still had many years in the past, of issues which needed to be fixed.

I think what you're proposing probably would have worked for reducing the communication issues in the future for any employees who left after that. I didn't hear of anyone who did that, but that definitely doesn't mean it didn't happen. Likely no one thought of it because I would guess most people didn't expect it to take as long as it did to fix. That the people who left while the recalculation was going on would just be a few more compared to everyone who had left in the previous 7 or 10 or 15 years (I think different companies came to different opinions for the time period they needed to retrospectively fix).