I wonder if some of these might have been civilian attire, with changed buttons and added insignia?
Edward Porter Alexander describes his trip to Washington after Appomattox, wearing "a U. S. Army private's overcoat, only dyed black instead of its original blue." < Gary W. Gallagher, Editor, Fighting for the Confederacy: The Personal Recollections of General Edward Porter Alexander. (Chapel Hill, NC: University of North Carolina Press, 1989), p. 547.>
If a young family member was going off to war, might a family modify some existing clothes into a uniform?
I do not believe that double-breasted frock coats were common civilian wear at the time. My guess is that because the early war Confederate uniform regulations (General Order No. 9 Uniform and Dress of the Army June 6 1861) proscribed short double-breasted frock coats for enlisted men, that some state units attempted to follow these regulations and adopted double-breasted frock coats.