I have seen same issues with date stamps a month apart...could have been transit time, could have been local distributor delays, could have been newstands issues... not sure anyone has really every researched in depth...
what we have to keep in mind is that the 4 color printing process that occured in the 1930's and 40's is relatively simplistic compared to today's technology... even Timely comics used former chesler/centaur printing facilities to produce books...so, multiple printers could have been (and likely were) used...but, they were still fairly regionally located together, so I have never heard, say, of there being superman 1's printed in NY and CAL in the same month...anyone else have more info, please share
only thing I know is that the arrival date stamped on a comic and the publishing date on the comic can be anywhere from 1-3 months apart. full date stamps