Not every refurb was issued to troops and saw "action". Sometimes the effects of time, moisture, cold, etc. can have an impact on metal (rust) and wood (cracks)... which necessitate rebluing, BBQ painting

, replacement stocks, etc.
I have a '52 refurb that I bought from Ki11ercane that had a mirror shine bore, and an absolutely brand new bolt, bolt carrier, recoil spring, etc... however the stock was replaced. I suspect it sat in storage, suffered some damage, and was then re-arsenaled with the better and stronger laminate stock. The bayonet was also re-blued and the gas tube was replaced, probably due to corrosion.