Thanks for the links Roygbiv666 and for the comments Yoc and Jon.
I guess my ultimate hunch is that comics from various publishers, due to their varying distributors and their varying local arrangements, may have turned up in (or been absent from) significant sections of the American continent. My guess would be that smaller publishers, who were distributed by smaller distributors, would have their comics absent from much of the country. I was just curious whether some publishers were able to get by, for awhile at least, with just regional NE U.S. distribution. Just idle curiosity.
As for Marvel comics in the Cleveland area in the 60's, it was my impression (which would support Jon's observations) that Marvel's distribution kicked up a notch within a year or two of launching the Fantastic Four and rejuvenating the super hero genre. I was in the Chicago suburbs by then and suddenly Marvel comics were available, while they'd been absent during the late 'stupid monster' period (or whatever one might call it) that immediately preceded Stan Lee's super hero re-boot.
I guess part of my curiosity is generated by wondering whether Dr. Wertham's anti-comics book was largely motivated by his access to smaller publishers' comics (which were sometimes more extreme) in the NY area, that never made it into major distribution in the rest of the country. In other words, was Seduction of the Innocent possibly a tempest in a Manhattan teapot? This is all conjecture and guesswork, so I have no serious evidence of any of this. Just an interesting question to pursue.