GM key knockout envelope
 

What year did they use this ?

Here's the key knock out envelope from a 1970 Camaro, so based on the PN sequencing, prior to 1970

The shape of the key makes me guess <1967...

or 1968, or even earlier....Joe

Square key one 3958690 - 1969 and later 70's
Octagon key one 3933878 - 1968 and older