Resolution

Check the Tax Year Settings Audit to see if the Next original bill field was changed prior to the start of the Actual Tax Billing.
Search in the Parcels program for the Tax, Parcel, and List no (Bill Number that is receiving a Preliminary Overbilled Adjustment and should not be).
If multiple records return with that search, there is possibly a problem.
To resolve the problem, if in a non-PROD environment, refresh the environment (install a recent backup of LIVE into the non-PROD), and start the bill run from the beginning without updating the Next original bill field in Tax Year Settings or set this to a value that is definitively higher than any bill number previously used.

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