there is no documentation of any military surplus rifle after they leave a factory.
1. they are made, packed in crates and assigned to a soldier.
2. if the soldier is KIA his rifle is either A) grabbed by the guy that killed him as a souvenir, B) grabbed by one of his comrades that needs parts/ammo/something better than what he was issued or C) grabbed up after the battle by whoever still controls the field and reissued to rear echelon troops/reservists/resistance fighters.
in any of those cases, there is now no longer documentation of where that rifle ended up at
3. if the soldier lives then he either A) is a bad little boy and keeps government property as his own, or B) throws it in a stack of other rifles where they will be repacked and shipped in to be refitted and repacked again in crates, where they sit in storage until A) wartime emergency requires them to be re-issued, B) they are sold off as military surplus or C) they are destroyed.
no matter the circumstances, there is always going to be a place where the paper trail ends. especially so in the case of 91/30s since tens of millions of them were made and they only have 4 digit serial numbers.