]Be advised, though, that there are a few missing pattern numbers in the blue book appendix list. For instance, since you ask about Iron Mountain griddles specifically, I've seen a 1079 IM #9 long griddle at a flea market already. (I'd've brought it home, too, but it was severely pitted.) The 5th edition Blue Book appendix lists 1077 for #7 and 1078 for #8, but that's as far as it goes. That's just one example.
It's the best list going, and even where it has gaps, it does an excellent job of establishing trends, which makes it easy to confirm whether or not the piece you're looking at is Griswold-made or not. But you might find yourself penciling in some additions here and there.
With respect to Iron Mountain, the general trend is that pieces with a p/n 10XX are Griswold-made Iron Mountain. On top of that, the skillets and handle-griddles have distinct-shaped handles, and the broken basting rings on the dutch oven covers are sorta distinct, too. I think that the Griswold section of the red book has better pictures of that.
And finally, to further confound your life, there are also two series of unmarked Griswold skillets that aren't garden-variety Iron Mountain, either. There's a size 7-8-9 run that have p/ns 754, 755, and 756, respectively. Those have the depth and dimensions of (Griswold-made) Victor skillets of the corresponding sizes, and I've seen at least two variations of 755, one with a more stylized "font" and one with a more blocky "font." There's also a highly coveted 3-4 set, both of which have 3-hole handles, with p/ns 668 and 669, respectively.
