Sorting magazines?

Some years back(1990's) I jumped on a deal for '20 GI 15 shot mags for $20'...the distributer promised scratches, dents and rusted mags plus some in excellent condition. That is what I got with the majority being in excellent or better shape. I have picked up some other GI mags and some 30 round mags too over the years

Anyhow...yesterday I dug out every M1 carbine mag I could find and sorted them out by markings and condition. Not very many repeats on manufacturers. The majority of these mags were assigned to various carbine manufacturers but some seem to be replacement mags and not manufactured specifically for one factory or the other.

Are there any mag markings/manufacturers that are particularly rare or scarce I should look for?...

How to tell post-war contract mags?....
I have several U marked mags that are near new and would seem possibly post-war....a circle B marked mag the same shape....and a couple excellent upside down K.I. Inland mags I thought could maybe be post-war

Thanx HT

WEP (Wade Electrical Products is scarce.) Any Irwin Pederson mag is hard to find. And IIRC, there is a very scarce NPM mag I think is marked IN. There are probably others too, but I can't think of them off the top of my head.

List by maker of WWII carbine magazines.

M1 Carbine 15 rnd Magazines

Yeh...that's the chart I used to ID makers and carbine manufacturers the magazines were assigned to.

No Irwin Pederson mags at all....I did identify one National Postal Meter mag but it's marked MN....I imagine my hard back Inland 30 shot may be the most valued mag in my stash

MN mags are quite common. I've got at least 3 of them. Its the IN that I can't seem to get my hands on.