I recently purchased 3 "Colt Factory Demo mags". Should the bodys be marked Colt? Also one of the bodies doesn't match the other two. It has 3 alignment stamps in the rib (front and rear)and 6 big deep ugly spot welds. It looks just like a sanchez mag I've got. The info on the bodies is as follows;
body 1)on outide is stamped 33710 and 6-91, on inside 91 k6 and 91 06
body 2)on inside only is 87 010 and 87 k10
body 3)The oddball body has no markings at all
The two bodys that match look just like an Okay mag I have which makes sense since Colt mags are made by Okay right? Anyone know of a good site with good info on identifying mag parts other than floorplates?

The Demo mags are just refinished USGI 30's. And being USGI mags, they could easily not be Colt bodies. I bought one a couple of years ago and it had glass-bead grit all over the inside to the point where it would bind the follower. I was glad I bought only one.

CDNN also has "Colt factory new magazines" does anyone know if these are legit colt mags? I'd like to have a few new colts if anyone knows a good source.

Colt's has never made any magazines, so any magaznie with a Colt's OEM floor plate could be "legit."  

Colt's contract 20 round USGI magazines were all built by Universal Industries and are labeled UI on the front.

Most if not all USGI magazines are built on the same equipment owned by the government and moved around to whoever has the contract.

-- Chuck

Weren't/aren't all Colt 30 rounders made by Okay? I'm pretty sure I read that somewhere. If so a 30 round Colt mag body could be identified by the slight differences between Okay mags and the other manufacturers. I know the same tooling was used by all manufacturers but I have noticed differences, mainly the welds. Also, at least one manufacturer stamped holes(locking tabs) partway through the front and rear(rib) of their mags between the welds. Identifie who made what welds,stamped holes etc. and we can identifie the origin of the mag body. Again, if anyone knows a good site with this info please tell.