The Mosin Nagant s usually went through upgrade when ever a newer model may come out.
1930, anything that goes through arsenal may get the latest upgrades of the 1930 version.
When the 44 carbine came out, the plants were too busy cranking rifles out to bother with refurbs.
Postwar, the big refurb was the '59 model. It was once pretty available in Canada but dried up for now. Pretty much long Mosin factory refurrbed and cut down to near mimic the '44 carbines except no folding bayonet. The '59s look a lot like the '38 carbines until you read the reciever. i don't remember seeing years converted though.
The SVT40s wee highly liked. Postwar, they were refurbed right away and greased and stored and probably didnt see daylight again until surplussed.
As mentioned, SKS were saved from a lot of wear and abuse by two factors.
Being semi auto and relatively smalll mag capacity saved the barrels from a lot of abuse.
Equally, being replaced by AKs saved them from years of abuse too.
We are lucky to get them in such nice shape.
Those chinese ones, we got a lot of brand new maybe some rebuilds that saw some abuse too.
What some satelite countries did to their Mosins, SKS and SVts are all over the board.