The offer is online only.
My feeling from reading your post is that Ovation has a maximun number of tickets to sell and when that allocation is reached they will cut it off unless of course, the allotment is increased. The box office will hold off assigning the actual locations until the date gets closer. Maybe not until the day of or 2-3 days prior.
Town Hall is not very deep, maybe 20 rows downstairs although it is four full seat sections wide rather than the usual three. I have sat all over that venue (the cabaret convention used to be held there) and even the far side seats were fine. Best available at Town Hall is much better than best available at the Music Hall. N.B. - I have never sat in the far side seats that are down close.
If the concert is three weeks away and Ticketmaster has B center seats available plus this offer is blasted out, it probably is not selling strongly.
Acoustically Town Hall is a treasure.
At twenty-five bucks a pop, this is a deal no matter how you look at it.
"If my life weren't funny, it would just be true. And that would be unacceptable."
--Carrie Fisher