Also understand that if this was not a commercial Colt, but a military 1911, there were many manufacturers of parts. Military 1911s that made it to retirement had possibly been rebuilt several times and could have frames from one manufacturer, and slides from another. Serial numbers could be struck over at armory level, to go along with their storage, and rack system.
The Marine Corps 1911's I had seen, often were collections of parts. Springfield slides on Colt frames were one example.
Here's a well loved example. Note that this was from a Marine armory, it has a frame that is stamped for US Army, has electro-pencil on the frame, a Springfield Armory slide, Colt commander hammer, King's beavertail grip safety and ambi safety, Pachmeyer grips, Aluminum trigger, Millet sights. Good things can come together in the hands of some military armorers.