Was wondering when aero levers came in. Seen old footage of Sean Yates using a pair, riding as an amateur in the mid-eighties, at a guess. Or would they have been modified non-aero ones back then?
People were certainly modifying standard levers by the late seventies, but I don't know who produced the first commercial offerings, or when.
By the mid eighties they were becoming quite mainstream. Shimano's aero groups from the early eighties (circa '82-'83) featured them. Pictures from the pro peloton seem to show 1986 as the tipping point - the year Campagnolo C-Record became available. Dia Compe aero levers are shown in their 1986 catalogue.
I have some Modolo Speedy levers from 1984 which can be set up either way. These have a small cable roller that fits where the normal cable anchor fits in the lever blade. The cable nipple sits in the non-aero cable exit. The outer runs out of the bottom end of the lever body as normal.