Most of the big agencies of the day were named in the same fashion as SCDP. J. Walter Thompson. McCann-Erickson. Doyle Dane Bernbach. Foote Cone Belding. BBDO which stood for Burton, Batten ....and I can't remember but should know seeing that I worked there for nearly 10 years.
Quite a few veterans on here, it appears - like myself. The entire series seems pretty on target, except the staffing levels - it took a LOT of people to churn those ads out, but that would make unwieldy tv. I was at DDB (Doyle Dane Bernbach) in the 80's and left after the merger with Needham, during the merger w/BBDO (Batten, Barton, Durstine & Osborne) to make Omnicom. We would occasionally chant "Hail, soldiers of Omnicom!!" in reference to empire-building mergers. Ad agency politics in the'80s were exactly as portrayed in MM.
Ironically, in college, in the 60's, all those initialed agencies were huge objects of derision for we incipient hipsters, before we needed to get jobs. Ahhh, youth.