Sam, you are right about the popularity of full choke back in the "old days"--although you're MUCH older than I am (about 3 years). A lot of those guns did double duty in the duck blind, then in the cornfields for pheasants. Back then, we hunted corn a lot for pheasants. Much "dirtier" than it is now, with a lot more weeds and stubble left after the pickers. Not nearly as clean to start with as today's corn, and significantly dirtier after the picker made its pass than after the combine cleans the field.
Also, dogs--except maybe the same Lab used for ducks--weren't all that common among pheasant hunters in places like NE and IA, where we had a LOT of birds. You wanted them to come down dead, and the belief was your chances were better of a dead bird with full.
Then came CRP in the mid-80's, by which time I had pointing dogs and was doing most of my shooting with a 16 choked IC/M--which worked just fine. I later found that for most of the pheasants I shot at, even less choke was good. If a bird flushed well out there, you could just let him go--because you knew there'd be another one, probably closer, before long. And it was just that much more opportunity to walk those big CRP grass fields and watch the dogs work.
