I don't know about BAM ever being considered a replacement for PBP although my rando exposure only goes back to the late 80's when I had wanted to do PBP in 1991 but I had an injury get in the way. I just don't remember anything other than Boston Montreal Boston as much of anything even close to PBP and that would be a stretch. I did the two years of SR before going to PBP in 1995.
I recall well organized brevets out of Boston (hanscom air base), NT (Harlem), Potomac Pedelers in DC, San Fran, Seattle, etc. Most people did not have email in 1993-95 and the internet as we know it now did not exist. It was a magazine telling you when the Brevets were and who to call (on the landline phone). Randonneuring was very different then compared to now but I really do not understand the idiotic comments from people who did not ride then. I'll just say we never had 5 controls in 50 km like some rides do now.