Probably the best method in determining the "official" status of questionable revenue stamps is to see what contemporaneous writers said about them at the time.
In this case, it turns out that the "F. D." (as well as the "S. T.") handstamped overprints on documentary stamps are entirely genuine.
They should be included in the Scott catalog as forerunners to the Bureau-overprinted stamps, exactly like the handstamped "narcotic" stamps precede the Bureau-overprinted stamps.
All that is necessary for proof of this is to go here:
https://books.google.com/books?id=DqhYtqLvD5YCand then go to pages 63 to 66.
The above link is
The American Philatelist, Volume 32, Number 3, December 1, 1918.
The handstamped varieties were originally intended to only be available from December 15, 1917 to February 1, 1918.
Of course, those handstamped stamps that are dated
after February 1 were clearly items that were still in stock at the exchange location at the time, and were just not traded in for the Bureau-overprinted varieties.

The moral of this story is that, in addition to looking for documentary stamps that are handstamped "F. D.," also look for those that are handstamped "S.T."
And also, maybe now Scott will list these handstamped varieties?
Jim
Most of the following stamps were acquired from one of the Morton Joyce sales.


