Why is it different?
 

I'm looking into buying a C4 that was manufactured in late 1990. I'm assuming it's a 1991 model year car but my question is why do some 1991 964s have an older style engine lid latch and some have the more modern design? Also the intake is black as opposed to metal. Did the company change these parts mid-year?

I thought the engine lid latch changed later, like '92-93.

I think the transition from the aluminum to plastic manifold happened early in MY91, because I've seen '91s with aluminum and some w/ plastic.

Another thing to note is the taillight seals. '89-90 have a rubber seal around the tails. '91-and-on don't.

Mine is a '91 and has the plastic intake manifold, the circular (old style) latch, and no taillight seals.

I'll have to check out the taillight seals.
Did the company make some changes mid-year?
I'm pretty sure the car isn't a '92 or later as it's manufacturing date is Oct of '90.
The car does have tear drop mirrors but that's probably a modification. Still has design 90 wheels.

I just read that Porsche made some changes to the car midway through the year of 1991. Does anybody know how to tell if a car is 1991 or 1991.5?