Your last sentence has me confused. You're talking about the U. S. Colored Troop, but then you say "It seems that a good number of the black volunteer regiments from the north were not given the U.S.C.T. designation and retained their state identity although they are considered part of Corps." What Corps are you referring to?
The Union Army was made up of many armies, e.g., the Army of the Potomac, the Army of the Tennessee, the U. S. Regular Army, the Army of the James, etc. Each of these armies were made of several Corps which were made up of artillery battalions, and cavalry and infantry regiments. The U. S. C. T. regiments were distributed among the Union armies and Corps, they did not fight as a single unit. Recruiting for the U. S. C. T. was a War Dept. effort; it did not affect the existing state volunteer regiments, with a couple of exceptions; namely, the 1st Kansas Colored Volunteers was changed to the 79th U. S. Colored Troop in December 1863. I can’t find the details right now, but the all of the regiments of the Louisiana Native Guard and some black regiments from Mississippi were also incorporated into the U. S. C. T. There may be others, but this was the exception, not the rule.
The Northern states were given credit for the U. S. C. T. regiments that were recruited and trained within their state, but the state did not participate in the recruiting because that was a Federal function.
If you look at the Order of Battle for any engagement (after May of 1863) of the Civil War, you will see that the U. S. C. T. regiments were co-mingled with the other Union troops at the brigade and division level.