If you overpay someone… getting that money back is a challenge.
To make it more complicated still, there was an element of “we’re not sure if we overpaid or underpaid” but there was also an element of “we gave person X an overtime shift but person Y was entitled to accept or deny that shift before person X would have even had an opportunity to take it”. That’s even harder to compensate for.
There’s no reason to leap to ‘stealing’ (which requires intent) from ‘ambiguous rules.’ Those ambiguous rules, incidentally, may have been agreed to — or even insisted on — by the union!
Not strictly for technical reasons, but definitely for political reasons. The client was potentially the largest organization in my province (state-run healthcare). Outsourcing payroll and scheduling with the potential of breaking the rules in the contracts with the multiple union stakeholders was a completely non-starter. Plus the idea of needing to do lay offs within the payroll department was pretty unpalatable.
Bring the problem back to our primary contact and they've got no clue what to do. They're on like year 2 of a 7 year contract and they've just discovered that their payroll department has been interpreting the ambiguous rules somewhat randomly. No one wants to commit to an interpretation without a memorandum of understanding from the union, and no one wants to start the process of negotiating that MoU because it's going to mean backdating 2 years of payroll for an unknown number of employees, who may have been affected by it one month but not the next, depending on who processed their paystub that month.
That was fun :D