Exactly. For example I have a Quality Hardware M1 carbine with a Rock-Ola barrel. Since it had the later sight that made the Rock-Ola stamp on the receiver difficult to read the seller assumed it was a Rock-Ola.
When I showed him it was a Quality Hardware he was upset as he now had what he thought was a mix master M1 Carbine. I had to explain to him "yes and no".
The receiver stamped with Quality Hardware and the serial number matched the production date stamp for the Rock-Ola barrel and Rock-Ola barrels are very common on Quality Hardware carbines as Rock-Ola was literally just down the street and supplied barrels to Quality Hardware.
Consequently the barrel, receiver, slide, etc were correct for the carbine as was the stock and handguard. It had probably not been swapped during an arsenal rebuild.
It did however appear to have had the typical post war rebuild with an M2 bolt, Type III barrel band, sliding rear sight, and later rotary lever safety, all of the above were commonly replaced in an arsenal rebuild to bring the M1 carbine up to a common standard. It did not have the potbelly M2 stock which was also a common replacement.
In short, it was a nice example of an uncommon Quality Hardware carbine that had a pretty typical post war rebuild.
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In the military I was at different times issued various M16"A1" rifles. One had a receiver stamped M-16 (originally a Colt model 604), an XM-16E1 (originally a model 603) and an M16A1 (a Colt model 614), all of which had been updated as close as possible to the then current M16A1 standard. Magazine safety fence differences aside they pretty well achieved it - close enough for standard manual of arms purposes.
I also saw various examples of H&R and GM Hydramatic made examples. At the time I thought it was unfortunate those interesting and unusual variants were updated to the M16A1 standard with comparatively few original parts.
But it's what the military does, they are not collectors. They would change the upper receiver, the furniture, the barrel, the flash hider, etc to achieve a common standard.
That was all part of the history of those rifles and it's part of the stories they'd tell if they could talk.
