Likely weren’t used as hard/wasn’t issued before Finn service. Many of the other mosins they got they received by trading with other countries post-WWI, those mainly being war captures of some sort. The American made examples literally could have still been in the crate in 1917 when the Finns received them.
Many US made M91 rifles never left North America. Some were used to train US and maybe Canadian troops that went out with the Expeditionary Forces, during the revolution.
I can remember seeing sealed crates of US made M91s in the mid sixties, in a US commercial warehouse. Some entrepreneur had purchased them and stored them during the mid 1930s. Alan Lever made a rediculously low offer on them and the old boy told him it was insulting, so goodbye.
That was quite the trip, that old warehouse was full of military firearms, mostly still in their crates. I don't know how many thousand were in there, but I was certainly impressed with what I saw and the numbers of unissued firearms all in one spot. This was just outside of San Diego, back in the day when such things weren't that uncommon.
During the late sixties and early seventies, many US made, unissued, M91 rifles were sold to the North American public as surplus. I believe Bannerman's sold off a bunch in the 1920s.
The Czarists had ordered the rifles but hadn't paid for them and they weren't delivered. The Soviets didn't want them or couldn't afford them at the time.
It's possible the Finns got some of those rifles, which were some of the best quality builds of that model I've seen.