Early purchasers were guaranteed a subsidy for a certain amount of years and some of those have ended. For this coming year, only those who purchased prior to January 1, 1996 get a reduced rate. Last year it was purchases prior to April 1, 1998.
I don't think you would be grandfathered in a resale. If you didn't close until after January 1, the owner would have to pay the dues. As part of the negotiations with the seller you could pay the reduced dues back to them.
The two different rates are $4.1685 vs. $3.3308.