Of course they have been using shellac on rifles for many years. Right around the end of WWII is over 60 years now. Doesn't make it the original finish on a WWII rifle. The recent wave of imports has been since the break up of the Sovieticon Union when many of the smaller states started selling off what they've held in storage. These do indeed have shellac as they've been refurbished.

Previous imports were either unrefurbished rifes, rifles from Spain or Finlandicon for the most part along with a few bring backs from other conflicts. They don't have shellac. Definitive answers on when the shellac started simply aren't there because the Soviets didn't make a practice of keeping good records of such things and/or sharing them with outsiders. I've talked with Russians who are active in historical presentations who can't answer that. Some leave the shellac on their rifles, some remove it. It's easy to assume they shellaced them all as it's what most people see but look at the earlier rifles, they do not have shellac. Refurbished, yes, but the refurbishment came after the war.

The shellac comes off with your fingernail, with almost no effort. Are you suggesting this was a protective coating suitable for the battlefield?