We just did an SSR add-on and they still prorate the dues.
For example, if someone purchased SSR today, dues would be pro-rated, probably beginning about May 1st, so the buyer would probably pay 8 months, or 2/3rds (that's 8/12ths) of the annual dues for that contract. If they set it up for monthly installments, they would have 8 months of dues being collected.
This would be the same no matter what use year month was being purchased. Dues are assessed by Calendar Year, not by Use Year.
The above applies to SSR and not AKV since the dues for AKV are special as the resort isn't open yet. I think all AKV dues begin on Sep 1st when the resort opens.