Again, no references on the RJ website but CheckMyTrip did find the booking and presented a seat map for the two BA numbered flights. Indeed, every aisle seat throughout the whole Economy cabin is showing as unavailable. Given that each pair either side is available I find it hard to believe they're actually occupied, so I'll keep fingers crossed that something becomes available nearer the time. I'll try a call to BA at that point to book.

Thanks for all the advice although I'll continue to look for direct flights for now!