Here is a 1968 Buick Skylark or GS tail lights lens. GM part Guide 43 SAE STDBR 68
I see no cracks in the lens and the chrome is excellent. This has been in a box in my garage for about 30 years. It don't think I am going to use it......
I think it is the same for lens for a 69 Skylark or GS.
Let me know if you need specific photos.
Thanks for looking.