Just found this thread, thought I'd add a datapoint: I have a Nishiki SemiPro purchased new in 1973 at West Side Cycles in NYC. Sugino Mitey Comp crank, Suntour derailleurs (GT rear), Dia Compe brakes, Araya rims, barend shifters.

On the bottom it says "no T6148Y".

Originally a 5 speed cluster upgraded a few years to a 6. But the Suntour rear derailleur became too problematic in its shifting and the barcons have lost their friction (and can't be fixed)...so its a winter project to change over to a fixie using original wheels/hub.