Rules for OTU points remain the same, even with the special.
So, it counts for they UY which is based on the trip you are buying to use them in.
Remember, you can only buy them when booking a trip 7 months or less.
Since both are Sept UY, but different memberships, it can be whatever you want based on trip dates.
For example, if you want them for a July trip and so does DH, then it would be part of your Sept 2024 UY for both memberships.
Not sure if this is your plan, but since you are within 31 days of the trip, you can’t buy them for a fake night, cancel, and then reallocate because anything you replace will be put in holding status.
Buying tomorrow can only be for trips starting August 12th or earlier.