Digital signature software like GnuPG might not be distributed as signed binaries under GPLv3 unless the archive signing key is included, by the looks of that, depending on what "unseal" means in court. [...]
Why should a signing key have to be included? [...]
To unseal the signature block. As posted, it depends what "unseal" means in court.
The signature isn't blocking anything here. You don't need the signature to install and/or execute the program in question, so there is nothing to `unseal'. If a signature key was required to run and/or install the program (license key, dongle, come to mind) then the key would have to be included.
Cheers.