Reservations at V&A are "true" reservations and not a priority seating. You are given a specific time (they will seat from 5:45 to 6:30 and again from 8:45 to 9:30) and there will be a specific table held for you.
Also it is not critical to reserve at the 180 day mark. The restaurant can seat 67 people and normaly has about 45 at a seating so it would be extremely unusual for them to be full, even a week out.