The discussion about the stamp brought two more scans from blog readers.
Here is an example in a rather grayish ink.
All characteristics of the genuine overprint are present.
I think this overprint is genuine.
Here is the scan of the second example. The base stamp is perforated, so it is not really the same rare combination.
The overprint should be the same though.
While I can find a lot of correct details the overall impression is irritating. It looks like the HH part is optically disturbed like being seen through a lens. There are also details I don’t like (second zero not smaller). For a final decision I need a better scan or the stamp in my hands. When I get the stamp itself I can take measurements and rule out alterations resulting from the used hardware (scanner etc.).
So keep it coming. This is free “scan opinions” for your stamps.