I get the impression Coritani had more land, and they had Lindum and Ratae... They were more developed, had their own coins, chronicled rulers names... Cornovii look to me like a buffer frontier between Wales, Brigantes and cental England...they could be rebels in Coritani province...
Of course, I'm saying all this sitting at the computer thousand miles from England, not as someone who's actually been digging up stuff, so I may be wrong :)