During what years where buildsheets sometimes placed into the cars during production. I am in the understanding that it was post 68, Am I correct or could they be found in other years also?

I beleive it depends on what plant the car came out of. I have been told the Arlington Texas plant did not put build sheets in cars like my LS-6 I am restoring, but other plants put up to 4 build sheets in various places through out the car. It's a good thing I have the original window sticker, or it would be hard to prove it is an original Black, LS-6, M-22 car.

Remember too that build sheets, or any other paperwork, wasn't meant to be left hidden in the car but rather tossed in the trash when the car done. That said, the build sheet could be anywhere in the interior, on top the gas tank, or nowhere. I had a gentleman just the other day send me pictures of 3 consecutive sequence Chevelle build sheets - all found in one 1970 Chevelle from Kansas City. Go figure...

FWIW I found my Arlington LS-6 build sheet under the passenger side sound barrier. It's in rough shape but legible.