Not to drag mud in but the obvious regarding rear mud guard seems to be over looked. The empty slot and hole. It's missing, was removed at some point, a bracket that was set under the fender. There's a rust spot where a washer had been used and compressed it there, around the hole. That's no coincidence, not accidental. The current bracket, copper rivet and the nut, do not have patina that's equal to the other parts on this bike.
@pedals-past I don-a wan-a open a can-o-worms but, your presumption of having a rivet tool to repair this, whelp, yeah works for today's logic but not yesterday. I mean, as example, heck in 50-60's plenty gas stations, plenty all across the US had all kin-a tools that plenty local kids could barrow, or a for a quarter and less, just have repair guy pinch in. Norman Rockwell painted a cover mid or just after WWII classic scene groups hanging around older station. As a kid and all through my teens or, out on rides say 1970 and few year more, plenty stations I could stop, patch a tire and or get a patch free, maybe a nickel or two at best, and install myself You could rely in this fact and mostly, no need to even have tools to fix a flat because only a few ritzy stations like full service 76 wouldn't welcome ya,. Back in the day, and long before me hit the planet, station attendants didn't sit at a window but, pulled two loads, if ya could not, in the least, perform some mechanical repair, up until, IDK say 1978-ish, you no get the job.
That fender was changed out from a bike that was mounted via the previous placement of currently un-used slot and hole. The evidence of it is clearly obvious in your photo.
Why change it? Looks at the grips, man that there is some wear, this bike has been ridden a lot! It's been used and cared for, for many many years. Ah, probably got nicked rear mud guard, bent up and care was continued with, maybe even by Schwinn dealer, who knows or cares for that matter.
Museum quality verses collectible? That depends on subject, Factory glory or relic of the past, depression era, pre-WWII, WWII through, IDK somewhere in the 50-60's. This bike served the owner as a transportation vehicle, loaded with all the equipment very well through the war and far beyond. Heck, a good tune up and it's ready to continue. I couldn't imagine a WWII and Korean vet, not liking and remembering any bike with its set up and durability, be it Schwinn or another. . With it being loaded with best in its class, It's a rolling museum that talks story, takes ya from hard times through the good, just as it is.
Oh, 1 more ting. Ya pulled the seat post out yet, another link. ? The original owner may have slipped paper or receipt in there.