93 fenders have larger wheel openings and the fender extensions are shorter front to back to compensate for this. The change was made in i think '90 or whenever the Pony rims came out. It's not a problem as long as you have both fenders...it's actually better if you plan on running 17s someday.
Yep 91-93 have larger wheel openings ahead of the wheel and below the molding. They will fit on the car, but fender extensions 87-90 will not fit 91-93.
79-90 have the same size wheel opening. 79-82 do not have holes for the fender extensions that came on 83-90, then 91-93. 91-93 have the bigger wheel openings for the 16" wheels.....which IMO is pointless. I put 17's and 18's on my 81 notchback and I had the old fender extensions on it too and they did not rub. This was with a 96-04 5 lug spindle conversion though. All that does is push the wheels out 13mm from stock, but you get it.