Having dealt with IL's least efficient bureaucracy before (and that is saying something!) I can tell you that you are unlikely to win. At the time the car was originally titled, ILDMV most likely used manufacture date or purchase date as the determining factor for the "model year". Since manufacture date at that time might have been 3 months before the change of the calender year...you are likely SOL.

Out of curiosity, why are you concerned when it sounds like they are willing to title the car without issue. ILDMV is one of the most evil of empires and the only state agency in any of the lower 48 that I have seen willing to turn over their duties to check cashing places.

Now that I vilified my mortal enemy, I will say that I had an identical issue with a 1979 BMW motorcycle in Oklahoma. In that case it was registered as a 1980 because it was sold and registered in June of 1980 but this motorcycle was in fact a 1979 big-valve R100RT that was just too expensive an sat for over a year before finally being sold. I never got that issue resolved but it did not stop me from tagging it year after year.

Mike