The blueprint for the modern unplayable rule came from:
1941 USGA. The player is the sole judge as to whether his ball is unplayable. It may be declared unplayable at any place on the course, except in a water hazard or in casual water.
1947 the USGA said a ball could be declared anywhere on the course. In stroke play a ball may be lifted from any place except a water hazard, penalty one stroke.
1950. Unplayable is...