Do you know which flight you are on?
BA may be waiting to see about demand on flights that day before committing you to a flight... You don't say when you are flying, either?

If it is within 6 weeks chase them up and say You wanted to reserve specific seats as it is a special occasion.... or similar... and you can only do that when ticketed.

Have you been to NYC before?
If not, take the transfer and enjoy the free tour. You might still be first on the vderop-off, somebody must be!!!