It looks like the magazine itself didn't have the copyright renewed back when that was mandatory, so the pre-1964 issues are out of copyright as far as the maga

It looks like the magazine itself didn't have the copyright renewed back when that was mandatory, so the pre-1964 issues are out of copyright as far as the magazine's own copyright goes (which is probably why archive.org feels comfortable putting them up). But yeah some subset of the individual stories are probably still copyrighted, so PG would avoid it.