I dimly recall the ability to borrow to complete ((part of) the last night was in the directory at some point.
Not since I've been an owner.
2018-19 directory:
"Should you decide to travel at the last minute and realize that you may need additional points to complete your reservation, you have the option to borrow points from your next Use Year during the Express Reservation time frame."
2014-15, 2011-12, and 2009-10 directories (use the exact same language):
"Should you decide to travel at the last minute and realize that you may need additional points to complete your reservation, you have the option to borrow points from your next Use Year. This option is available when you are booking a reservation during the Express Reservation period, 90 days or less from your check-in date."
However, prior to 2017 the points credit pool functioned essentially as a borrowing tool. If you needed to "borrow" points from a future year, you'd just credit pool some or all of the points from that year and they'd become available for use immediately.
EDIT: As an example of how established the credit pool was as a borrowing tool, there was one year when I credit pooled points from a future year in order to use them in a current year, and it wasn't until after I'd done it and paid the $39 fee that I realized that I could have simply borrowed the points, because it was inside the 90 day mark, and saved the $39.