Hello,
I have just downloaded the 3.0b1, and finally was able to register it (bought superduper I dunno how many years ago).
However I had not yet used superduper at all on many iterations of the High Sierra betas and GM candidate. When I launched the 3.0b1 (sure wish I didn't have to use the usual to open it, e.g. control-cmd open) and tried to register using the Register menu item, there was no place for the name and serial number.
After relaunching a couple of times with no success, I downloaded the 2.9.2 version, registered that and then the registration showed up in the 3.0b1.
I dunno, but I think this might be a bug to fix.
best regards,
Philip Noguchi