I would venture to say that pre 1962 or so a hunter who used a folder was using a slipjoint. A lot of single blade "hunters" (typically a large "coke bottle" or "clasp" knife) and 2 bladed "trappers" (regular and bullet or bullnose patterns (Remington "Bullet" patterns) were and are still seeing use for dressing game and I would bet muskratts and stockmen are/were also used especially on smaller game.