Further update:
I tried the slow rebuild with no change.
I contacted PG Music Chat and sent them screenshots of styles - he advised that "19% is the correct number for the Pro version of Band-in-a-Box". However he did not have access to the full Windows list for me to see and asked me to email a request which I've done to both sales & support. Awaiting a response.
It's a bit disconcerting to find that what seemed a basic query is not so basic after all. It's such a brilliant package but not straightforward for non- techy peeps.