From what I know from a distance about Mobile and Pensacola, I think it's fair to say that they're a little unusual as DMAs go. If TV stations were being allocated to the region for the first time today, instead of in the 1950s, I think it's likely that Mobile would be its own DMA separate from Pensacola/FWB - and that both would thus be smaller markets than the combined Mobile/Pensacola DMA is now.
I think this is likely true but maybe for a different reason than what Scott is thinking.
Keeping in mind that I'm an engineer & my opinion may be colored by that...
... Note that Mobile was only allotted two VHF channels, and Pensacola only one. Those of you who are under age 40 or so may underestimate just how important it was to be below channel 14 in the early days of TV.
Imagine it's 1958 and you've just moved to Pensacola. You bought a new TV set (which only comes with VHF, UHF tuners won't be required for another six years) and you need a VHF antenna to get Pensacola's most popular station, WEAR-TV channel 3, ABC.
You hook it all up & find you also get pretty good -- near perfect -- pictures from the two Mobile stations, WKRG-TV channel 5 CBS and WALA-TV channel 10 NBC.
Are you going to spend more $$ for a UHF converter & antenna so you can get a *partial* NBC and *partial* CBS schedule off WPFA-TV channel 15? Probably not...
which means most viewers in Pensacola are watching Mobile stations, and the two cities are going to end up in the same market.
By the time the technology of UHF improved to the point where WPFA's signal (and UHF receivers) would be competitive, it was too late.
IMHO, for Mobile & Pensacola to have ended up as different markets would have required the cities be far enough apart (or separated by a terrain obstacle) such that reception of Mobile stations in Pensacola was not practical with the antennas most viewers would be able to install.
I would suggest a similar situation applies with the assignment of Randolph Co., Alabama to the Atlanta DMA.
The CBS affiliates in the Birmingham and Anniston markets were UHF. Chances are most viewers in Randolph County couldn't receive CBS from an Alabama station even if they wanted to; their only choice for CBS was WAGA. With one of the major networks simply not existing on a Birmingham-market signal as far as Randolph Co. viewers are concerned, there's little doubt that a majority of viewers would be watching Atlanta stations. And again, by the time improved UHF technology made reception of UHF signals from Birmingham practical, cable had etched viewing habits in stone.
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As for the retransmission disputes...
again, if you look at history I think the cable industry may have shot itself in the foot.
For decades, the cable/station relationship was controlled by a combination of must-carry and mandatory retransmission consent. Cable operators were required to carry every station that delivered a decent signal, but the stations were not permitted to charge for that carriage.
If that model had survived to this day.. cable operators would be carrying the same set of OTA signals they're carrying today, but they wouldn't be paying the stations.
But... back in the 1980s... cable operators decided they didn't want to use their (then technically-limited) channel capacity to carry low-rated independents and duplicate affiliates of the same network. So they went to the Supreme Court & got must-carry ruled unconstitutional.
With must-carry gone, the justification for requiring free retransmission consent was also gone. And the door was opened for stations to charge.
As much as we may (or may not) believe the major OTA networks are on the way out, ABC/CBS/Fox/NBC affiliates continue to be by far the most popular channels on any system. Any multichannel provider that's missing one of these networks is going to be at a significant competitive disadvantage, and as much as we may decry the difficulty of switching, most viewers are willing to switch if they think another provider will provide a better deal. (including *all* the channels they watch)
Multichannel providers could have *still* had the major networks for free, if they hadn't upset the applecart 30 years ago...
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Anyway, to come back around to the beginning..
I think probably today, Mobile & Pensacola could indeed each support a full set of network affiliates*. Due to technical limitations 55 years ago and the development of multichannel providers 35-40 years ago, we'll never find out.
* especially as chances are, at least one duopoly would be involved in each market -- there would be four affiliates but two or three owners.