OK, made me look!
The number on mine is (logo)-20229
I bought it from the buddy of the original owner (the bike was originally raced on the Helotes bike shop team) and he said it was a '89.
Maybe the last number represents the year, but who knows.

On the seat clamping bolt, mine is a normal stainless Allen socket screw and threads into the far side.
The far side is flush, while yours maybe has something sticking farther out? A heli-coil should work if it's stripped.