Here's a pic of my VERY unfinished imperial guard. I'm waiting to get to work on it until the new codex comes out hopefully in may. It has Valhallans, Catachans, Cadians and my own mix of cadian/catachan parts (not to mention a squad of vet. Squats!). I'm gonna suggest they are a regiment composed of the remainders of other regiments... kinda like the lucky/unlucky survivors of past campaigns. Hard to make out in the pic, but there is 1 Leman Russ, 3 Chimeras, and 6 Sentinels in the pic too.