The XMC models finished in 2012 - they had alu crowns/steerers with carbon lowers, with 32mm stanchions
XMM continue and feature alu crowns/steerers with magnesium lowers and with 32mm stanchions
XRC were alu crowns/steerers with carbon lowers OR carbon crowns/steerers with carbon lowers, all with 28.6mm stanchions.
You can now see why DT are rationalising on the numbers of forks they produce!
I do have a set of 2012 XMC 120mm 26" forks (6months use) I'll be selling very soon - message me if you're interested!
Thanks very much for the information, definitely clears things up. Interestingly enough my question was prompted by my sale of a DT Swiss XMC 100mm fork (26") currently listed on ebay.