NACA had V-G recorders back in the 1930's. Prior to about 1950, they were dry dampened . That report is about the new oil dampened ones.
As to slot head screws.....They were on airframes, instruments and furnishings. I've got stuff on both my L-5 and AT-21 that have slot head screws, and they were built in the 1943-44 period. The specifications for that hardware dates years prior to that. I don't have the spec number for the ones in the cockpit cover for the AT, but there are over a hundred of them in it, alone.