Just pulled the radio- mystery solved. My "1991" 300TE has the 1480, not the 1432 as the 91-93 vehicles should have.

The car is titled and registered as a 91, so your clue about production run got me to look at the door jamb plate for the first time ever. You guessed it- production date 8/90

I never knew. But now, easier to upgrade radio to something new

Thanks mbdoc.