Hey there! Welcome!
Field WK.YEAR in USG.AUDIT.XREF was last updated for Version 16. The validation code change you made will work until you try to enter 2011.
Personally, I would update the limits to 20 and 2020, respectively, and report the bug and temporary fix to Activant. It will be something to check on the next upgrade to see if it was fixed.
--Tom