Ted, the NID was pretty much a complete redesign, succeeding the Flues. Dating from about 1925. The Model 12 was designed . . . well, it had to be designed prior to 1912, which makes it older. Unless you mean that a side by side, generically speaking, is an older design than a pump.
It does go without saying that the rib won't come unsoldered on a Model 12, however, if it has no rib. I'm not a pumpgun guy, so I don't know how they attached ribs on those guns, although I know some ribs on pumps (and autos) do come loose.
I've owned a number of NID's, and I never worried much about hunting them in nasty weather. (Nearly all of mine were Field Grades.) It was a strong enough design that John Olin turned to Ithaca to build guns for his 3 1/2" magnum--rather than using his own Model 21, which is famed for its strength.
