SC 1903A Parts Some Parts Miss Match

After looking at a alot of 1903A3 and seeing few that are all correct for various unknown reasons and when trying to find out why the typical answer is "well it was an arsenal rebuild" after the war. Not all miss match show arsenal rebuild marks, so could it not be possible that parts like say the bolt was mixed up with others in the field during cleaning etc.? I know they were not front line duty for the most part, but they still were cleaned and misery loves company. Not sure GI's were taught not to mix and match the bolts?

In particular, this comes up after buying a 03 from a 90+ year old gentlamn who swears he brought it back, has pictures of him carrying it, but the bolt is Rem and the rifle is SC.

Maybe I am oversimplifying. More knowledgeable people have thoughts?

Generally speaking, the stock is where a "rebuild mark" as you refer will be. But we all know that the stock (any parts) is subject to change or modification by any person it's ever passed, so it cannot be a definitive answer to having been through rebuild or not. When it comes to the parts there are primarily two indicators, first is mixed manufacturers and second is finish of said parts vs original. So, if your rifle's composition is of mixed manufacturers parts with mixed indications by finish then its most likely a parts rifle. If the finishes are consistent with rebuild finishes then it's been through rebuild. But based on your description it's definitely not original.
Keep in mind, original finishes are a combination of bluing and Parkerizing on certain parts, same goes with arsenal rebuild except more parts got parkerized. Only way for any here to make an educated guess is for you to post pics. Be skeptical about the "brought it back story" if he did then it's probably on Uncle Sams/ TACOMS list of give us our rifle back or else. Neat story but most of the time incorrect.

Thanks for the reply, Randy! I assumed the bring back was incorrect as that seems unrealistic given the weapons size. A 1911 maybe easier but still risky. Anyway, given it look slike only the bolt, complete bolt, and the one barell band appear incorrect, seems it might be worth finding a complete SC bolt and the barell band to make it right again. I's say the barell band becasue it's parked and the most forward one it blued, as it should be. Are these parts difficult to find? Serial # dates it to Jan 1943 and barell is 3-43, Thanks