As I progress (very slowly) through the route history of Black Prince, it is always satisfying to fill in a part of the jigsaw which has proved difficult to obtain information about.
The 98A has been one such route which has proved difficult to confirm, but with huge thanks to Dave Lee, who has provided several historical timetable leaflets it is now possible to trace what happened (at least partly) with this route.
The information has been added to the website at the link here https://www.blackprincebuses.co.uk/98a
I shall continue to investigate this interesting service and post updates as required... meanwhile, does anyone have anything to add?... If so, please use the contact form :-)