I suspect that there is a massive amount of WW2 weaponry that disappeared into hiding places during and after the war.
I agree. They had two major wars sweep the continent in thirty years...plenty of opportunity to pick up a dropped Mauser or Garand and hide it in the barn. And since they were expecting another Great Soviet Invasion for forty years after, plenty of time and motivation to scrounge up more arms and keep them hidden.
I’ve seen pictures of “battlefield pickups” in private hands in France and Belgium that would being a small fortune if they came to the States.