Yes, I have seen them, the same shims (approx. 1 1/8" square, variety of thicknesses, no "tail") as used on the upper rear fender attachment bolt at the base of the windshield post, used on the cowl grille panel - to cowl panel mounting points; the most I have seen are 2 per hole. as with all GM "shim cars", some cars had them, some more than others, and some did not. I love these cars, but they are certainly not a "Lexus" when it comes to fit & finish.
The cars that I observed were apparently untouched cars, 67-69 Camaros and particularly 68-77 Novas. I have seen more Novas with the shims, and they are basically the same car with this in regards.
Regarding the headlamp mounting to core support shimming in your other posting, no, never seen this, but possible. I would check the mounting points on the core support for distortion; a length of 2 x 2 wood block and a properly administered hammer blow could also be what you need instead of a shim in this area.
Make sure you are installing the fender correctly; sometimes (ie: vertical rear upper fender-to-cowl attachment) the use of too many shims in one area can cause the need for otherwise unnecessary (cowl grille) ones elsewhere.
Hope this helps.