If your banked points are 2017 points banked into the 2018 use year (12/1/ 18 - 11/30/19) they expire 11/30/19, and by the time the contract closes in September or later the buyer most likely couldn’t find anything to book before the banked points expire.
Indeed, if I were selling a Dec. use year contract this late in the use year I’d be banking the 2018 points into the 2019 use year (12/1/19 - 11/30/20) before the 7/31/2019 banking deadline, so that they wouldn’t be lost due to the lack of availability between when you close and 11/30/2019.
Hopefully you didn’t finance your contracts, or if you did, the resale prices have gone up enough to cover what you owe and you won’t need to bring money to the table to close.