Just got an update from Suse:-

I'm happy to inform you that the ability to remove NCC-registered systems from SUSE Customer Center is finally there.
When you remove systems, your subscriptions' system totals should be updated.

Thank you for your patience.
Please report any further bugs that you encounter in SCC.


Greetings,
SCC Team.

Hope this is of interest,

Regards

ChasR.