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.
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.