Skimming through the answers I don't see this mentioned but back in the '80s and I am sure the '70s as well there were not enough complete component groups to build 15 different models of bikes all with one group. there fore alot of mixing was done to get price points. so just because a bike has say a nicer quality SR crankset and Universal or Weineman brakes and Campi NR derailleurs does not really mean tthe derailleurs were upgraded.
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk