I start with when will my trip be, then I figure out which points I can use to book that trip. I can always book 11 months before day one of my trip - use year only impacts which points I can use;
For example, say I own 100 points and have a Dec. use year. I want to go to WDW from 11/20 - 11/27/19. My villa will cost 300 points. On 12/20/18 I would make my reservation using points from these use years:
100 points banked from 2017 (runs from 12/1/2017 - 11/30/2018 - I would have already banked these because if I hadn’t they would have expired, if you intend to bank you must do so in the first 8 months of your use year)
100 points from 2018 (runs 12/1/2018 - 11/30/2019)
100 points borrowed from 2019 (runs from 12/1/2019 - 11/30/2020 - I can borrow these at the time I make my reservation)