Well you have to remember there was a war on, and a big one. Things in the way of pistol production didn't always happen like they were supposed to.
Then matters were complicated more after 1945 when Uncle Sam stopped buying new pistols. Thereafter the older ones were rebuilt if they were deemed to be unserviceable. The frames were retained if they were sound, but everything else could be, and sometimes was replaced. Thus the slide on a particular gun didn't necessarily mean that that was the company that made the frame - or for that matter, other parts.
The big $$$$ you see only apply to a pistol that is 100 percent original, and because of all the rebuilding that went on those can be hard to find. On too many occasions I have seen someone spend big bucks, only to discover later that they have a hybrid.
Mis-matched guns are not necessarily bad, as some of them are collectables in their own right. But before you lay down any money you'd better be sure about exactly what you are buying.