Okay, makes sense.

No, it is widely understood as a means for reproducible builds and specified at: https://reproducible-builds.org/docs/source-date-epoch/

SOURCE_DATE_EPOCH is NixOS specific?

Well, I had simply accepted that the rule for defsincdate is always triggered. I looked a bit more into it, and the cause for triggering is that Nixpkgs patches dirmngr.texi, hence defsincdate is cleared by the rule above and the fallback behaviour is triggered.
But this also means my suggested patch wouldn't help here as the modification date of dirmngr.texi would be picked up.

Looking at the rules I do not understand why we have a problem here, the rule

I think an option to ignore certain files is a better way to do this. I'll give it a try.

Cool. Falls du einen Korrekturleser für die neue Fassung brauchst, sag gerne Bescheid. Ich hab da Erfahrung …

erstmal vielen dank für das Feedback. Ich habe momentan als Aufgabe ein neues Benutzerhandbuch auf Basis des Kompendiums zu erstellen und werde da die Hinweise auch mit Aufnehmen. Technisch ist sowohl der Inhalt als auch die Art wie das Handbuch erzeugt wird nicht mehr aktuell, wir brauchen da dringend etwas neues das wir auch online stellen können.
Sollte noch in diesem Jahr passieren.

Thanks for the patch, applied!
You are correct the NEWS file states that this was added in 1.9.0

@sarman: Your question is actually a support question and not a bug report. Please read the documentation, use the public help channels (so that other can also learn from the issue), or get in touch with a commercial support provider.

I think that what you want is adding --batch option. In the gpg manual, we have:

--passphrase-file file
       Read  the passphrase from file file. Only the first line will be
       read from  file  file.  This  can  only  be  used  if  only  one
       passphrase is supplied. Obviously, a passphrase stored in a file
       is of questionable security if other users can read  this  file.
       Don't use this option if you can avoid it.

Hello Team,

For operations which require private key, it is needed to unlock private key.

Thanks. Fixed in stanble and master.

This was already fixed with version 2.2.5.

This was also raised for (hopefully) wider discussion on the IETF mailing list.

I am in charge of editing the current OpenPGP draft, so I will for sure keep an eye on that issue. If would appreciate if you can post your report also to openpgp at ietf org.

Thanks, fixed in master.