Depends on which model. According to the 1979 catalog they were already being used on the top models. Over time this trickled down to the lower range models too.

I'd also be curious when they had first stopped using them. Through the 1950s and even into the early 1960s most bikes came with extensive braze-on guides. Then after Cinelli successfully got away with selling just totally stripped down frames with no useful braze-ons, gradually all the other manufacturers decided to save money as well and also began to skimp on these basics elements.

Custom made bikes had never lost their braze-ons, and by the early 1980s people began to look for them as an indication of better made bikes... again.