That is not my experience, which started in 1964, and included US midwest, Europe, and US East Coast.Octos were fairly common by the early 1970s, at least on more demanding dives like wreck penetration and decompression dives.
For fun, I found this 2006 SB post, Alternate reg from the left or the right?.
The following is purely anecdotal, however, others on the board of my vintage may be able to corroborate this with their own experiences.
In 1980 and 1981 'octopus' second stages first began to be seen in California (La Jolla) and NAUI/PADI course literature as widely distributed as (Marine bases on) Okinawa and Guam in the South Pacific. Until that time "buddy breathing" off one second stage had been the standard OOA response. The "octopus" second stage was touted as safer than buddy breathing.
[Secondary second stages may have been in use earlier, but not widely. In a cave class we were informed that during the early 1970s some cave divers used a second second stage on a long hose to allow two divers - a donor diver and an out-of-air recipient diver - to pass single file through narrow passages and restrictions in caves, where buddy breathing would obviously not have been possible. It simply took time for this concept to migrate into the recreational diving realm...]