Re: It's a hand hole, isn't it?
It is unlikely the inner cover was as thin as it is today. it certainly was not made of plywood. it didn't exist yet. It is more likely the inner cover was made of wood an inch thick or more. My home was built in the late 1940's. the entire ceiling is made of 2 inch thick tongue and groove lumber. today the same woudl be about a half inch thick and still not used as a ceiling.
Significant Minority vs Insignificant Majority, 20% of causes produce 80% of the effects.