Well we have answered that part of the question that appearently those were all White regiments, which I do not see as being unusual. But appearently there were black regiments raised in Tennessee also. Not all Black regiments were U.S.C.T. until reorganization in mid 1864. Remember the 1st, 2nd, and 3rd Louisiana Native Guards. And even then, was such units as the 54th Mass. ever reorganized as a U.S.C.T. regiment?
As a matter of history the vast majority of the 178,000 to 250,000 blacks, I would say in the upper 90 percentiles, that were members of U.S.C.T. regiments, were slaves from the southern states. The majority of those probably came from Tennessee, Arkansas, Mississippi, Louisiana, and Virginia and maybe coastal North Carolina and South Carolina as those were the southern states first under some form of Union occupation and had large problems of what to do with contribands.