Hi

I assume your ID (68 GTX) is the same is the car you are asking about, I did not see mention of the year/model car you are referencing. If it's a B-Body (GTX) then you are right and it should be there..... If it's an E-Body then that's a different story.

If it's that important (only if it's really important)... I would take some lacquer thinner, a rag and maybe some sandpaper and take off the paint and any filler that may be covering it up.... Another hint would be to look for clues as to whether or not a replacement quarter panel was ever installed. That should be pretty easy if you know where to look and what you're looking for.

If it's a car that you own and enjoy driving....and you're just curious... I'd just enjoy it and keep driving it !

Good luck