You made a pretty broad statement that was not attributable to any one country.
Many (most) sniper rifles were arsenal manufactured specifically as a scoped rifle ab-initio when assembled.
That was true in Russia, and it was true elsewhere as well.
Contemplate M1-D, Springfield, Mauser, etc. The scope mounts are not something that are attached after the fact. They are integral components of the rifle system and need to be assembled when the weapon is either manufactured or arsenal remanufactured. There's no "cherry picking and then modifying after the fact" as a rule. You build them to spec, and they they meet spec.
Nagant Snipers, were manufactured at the arsenal (or remanufactured at an arsenal) with scope mount holes drilled and scope mounts attached, and they were test fired after the fact to ensure that they met specifications.
My own example, BTW, is a Hungarian M/52, propably the finest Nagant version made. I still rate it a "So what" when compared to other similar hardware. Cheek weld? You must be kidding.