The points are essentially always "there." The date where you trip falls determines what year's points you will want to use.
So if your trip is in September 2026, that falls into your 2026 UY allotment of points. If you plan to book 11 months in advance, you would be booking in October 2025 but you will be using your 2026 points since that's when your trip actually occurs.
The 2025 points you rented out would have been for travel dates between June 2025 and May 2026.
2026 points will be for any trips you take June 2026 through May 2027.
Hope that makes sense.
Oh, and you could also "borrow" from the next years points when booking, if you wanted. So if you needed more points for your September 2026 trip, you could borrow from your 2027 UY. (But, once you borrow or bank any points, they stay in the UY you put them in forever and can't be moved back. Therefore, expiring at the end of that UY.)