jgrass,
Without seeing it, I cannot comment definitely, by I have event covers by Fidelity in my collection for both Dec 7 (Japan) and Dec 11 (Germany) as well as WWII event covers for numerous other significant events. The OP is right that the cachets on the covers could not in most if any instances be produced prior to or on the same day as the event. I've always assumed that when a significant event occurred, the producers of these patriotic covers would rush to the post office and get BLANK covers postmarked that same day, and then add the artwork or text commemorating the event afterward. Some of these are possibly faked, however, especially those with the popular "VICTORY, Vermont" postmark. But most are legitimate philatelic creations. Sherman's catalog lists over 12,000 different WWII patriotic covers.
As for the postmark, there was a difference between "defense bonds" and "war bonds." Defense bonds went on the market in May 1941. FDR had already pushed for major investments in "National Defense" before we ever entered the way and a three stamp set of "National Defense" stamps were issued in October 1940. Here is a page from an exhibit showing defense and war bond cancellations:
Posted 02/28/2018 7:26 pm
