I noticed that in CBSubs Geographic Zone in European Union there is no Croatia and there is still GB (id15) (same as on your Demo page)
I added HR and removed GB on my website (EDIT ENTRIES in Collection of EU Countries -> checkbox and Delete GB)
Everything seems to work except for the disturbing red message in:
CB Tools: Check CB plugins database: Results
CB plugin "CBSubs Tax" database structure differences:
Table #__cbsubs_geo_zones_entries Rows id = 15 do not exist
The CB plugin "CBSubs Tax" database structure differences can be fixed (adjusted) by clicking here: Click here to fix (adjust) all CB plugin "CBSubs Tax" database
The repair causes GB to return to the EU with id 15 in database of course ...
I wanted to make sure that I do not have to worry about this message and that the database may be missing selected id after removing the item (country).
Alternatively, is it possible otherwise to remove a country from the Geo Zone without triggering a red "missing id" message in CB Tools: Check CB plugins database?