The ORIGINAL assembly line part numbers for the 1969 Z28 emblems were 3949681 and 3949682. The casting number underneith will say 3949681-LH and 3949682-RH. Service replacements were part number 3957935 and 3957936, and will say 3949681-2 underneith.
In the April, 1977 P&A you could still get both the 3957935 and the 3957936. In the April, 1981 P&A you could only get the 3957935, so they discontinued the 3957936 sometime between these two dates. Sorry I can't narrow it down more.
Since I'm a packrat and hoarder, I still have the new emblems I purchased in September 1978, as well as the order form which I've scanned and attached (if I did it correctly). The order form shows both 935 and 936 parts being ordered, but the 936 beiing replaced/substituted by the 935 part on delivery. I pulled the parts from the boxes and both had the 3949681-2 pn on the back. Since my original emblems are off my car and in bags, I then checked those and found both to have only P-394968 on the back. My car is a late 09C production.
Gary / 69Z28-RS