Another Person Wanting E30 M3 Information :-)

I'm considering the purchase of a '90 M3 that is in good condition.
However, the emissions sticker on the left front strut tower says
the car meets EPA emissions requirements for 1991.  The build
plate in the door says it was made in 4/90, and the VIN decodes to 
a '90 M3.  I haven't checked to make sure that the VIN on the dash
matches the VIN under the hood yet.

So, any '90 M3 owners have the '91 emissions sticker on their cars?

Any good theories on how this could happen?  Accident in '91? 

Rex Tener
1988 Acura Integra LS-SE