WT+ seems to be getting increasingly popular, particularly on the North Atlantic. A lot of companies, mine included, have made WT+ or VS Premium Economy the travel policy class across the pond.

Seat availability is tighter, but no side seats six weeks prior sounds odd, there are no rules about seat pre-allocation, it's a dark science. The single seat is lucky catch.

Try calling the reservation centre, at least they can tag your booking with a preferred allocation. An aisle on the centre four is OK, I have often had a spare next to me.

g'luck.. ^