A method to guesstimate when things were done is to look at how the finish and wear varies or matches. For example, here many of the parts are worn to bare metal. The barrel has an almost new blue color. That was installed later.
The rear sights adjustments often wear and the sight gets replaced. My casual observation is most replacements are "R" stamped.
Also armory rebuilt rifles will have that armory stamp on the stock. That is in addition to the original inspector stamp. Then stocks get swapped all the time.
Stocks and everything else. Look on ebay, every bit and piece can be found.