by '79/'80 most all road bikes went to 126mm spacing (12- or 14-speed).

'78 was about the first year this was done (per my experience anyway). never had nor run into an '80s bike with 120mm rear.

the again ... all 12-speed bikes provide, at most, 10-speeds, because you never ride in the outer limits of the chainline (big chainring/big cog combo and small/small combo).