It's a question that comes up a lot, so it's definitely fit for public consumption. As a general rule pre-WW2 slides don't hold up for as long as a post-WW2 slide will, as the Austempering method of heat-treating parts wasn't fully developed and implimented until the late '40s. Austempering and other newer methods heat-treat the ENTIRE slide, which is why you gunsmiths cuss a lot when trying to mill a recently-made Colt slide for Bo-Mars.
Before then, slides were intentionally left soft to allow for machining operations. In 1925 the front end of the slide was heat-treated via the well-known heat n' quench method. Later in 1943 the slide stop notch was flame hardened as well. On these older slides, to prevent premature breech face wear a hardened plug was installed where the firing pin hole is. You can easily see on a GI gun the dark circle surrounding the firing pin hole. The locking lug area was still left unhardened, and as a result WW2 and earlier slides will often display peening damage to the lugs if the barrel fit wasn't proper or the gun has seen a lot of rounds.
All this shouldn't scare a person from shooting an older 1911 or 1911A1, but keep these facts in mind and go easy on it. Furthermore, in my opinion spending the cash on fitting a tight match-grade barrel is a waste because the soft slide will wear more quickly and you'll lose the accuracy you paid for after so many thousands of rounds. Or worse yet, if the barrel isn't properly fitted the slide lugs will be peened to death in short order.