Plain old plywood of 1932 is a lot different than plain new plywood today.
The three important factors to consider are surface finish, internal strength with lack of voids, and type of glue.
"Old School" tended to use more-thinner layers of veneer, and the veneer tended to be about the same quality as the exterior with only small void patches. "Old School" common glues were not water resistant enough for exterior application, hence the need for different "interior" and "exterior" grades.
Modern plywood tends to use trash wood for the interior plies and allow large voids and are often only 5-7 plies. Modern glues work much better than old school so there is no longer a cheaper interior grade.
Common plywood is graded by 3 letters such as A-B or A-C-X. A is sanded surface, B is not, C has a lot of voids, and X is crap. Two letters indicate the interior plies are the same grade as the unsanded side. The third letter indicates the core plies.
If you make your floorboards at least go with a marine grade plywood with at least 9 plies. This should be about the quality of "good old plywood". A better grade plywood available in the Pacific Northwest is a "baltic birch" from Finland or Russsia, which is a 13 ply.
