The issue is credit adjustments. An invoice was entered in one month but is credited in the next month. The tax rate has CHANGED. The invoice needs to be credited EXACTLY for the tax amount that was charged in the prior month.
The environment is GP2010
The resolution is when creating a return, customer needs to go AvaTax Override Line Details, by clicking on Additional in Sales Item Detail Entry page
The cause is they were calculating tax on a different day from the original sales day