I've had a couple issued non-refurb WW2 91/30's - both were hand selected when Finland dumped its Mosin rifles on Canada bout 10 years ago. These were rifles the finns picked up and put into storage, they had not SA capture stamps or anything.
In both cases, the stocks were just oiled - no shellac. They looked like a WW2 birch-stocked Savage Enfield.
My opinion is the garnet shellac is a cold war "thing".
I agree, I am betting the wartime finish was some type of oil. look at a picture of a range used 91/30 and you can tell obviously in photos where it has worn off/ flaked/ chipped in areas just from use. Look at the thousands of images/ footage of them actually being used in WW2 and none of this is noted, and you cannot see the shininess of a shellac.