They are. I suspect demand has them subcontracting some (not all, thus the different number ranges) of the frames, either raw frames in for forging, or forged frames contracted out for finishing. I suspect the latter. I know Turnbull has done several finishing runs for Colt.
For accounting purposes, Colt would list itself as a "source" for frames, with the subcontractor the 2nd source. The subcontractor might even be Colt Defense, on the other side of the building, but maintained as a seperate buisnes entity.