Member Services uses banked and borrowed points first when they make a reservation.
How about a visual? Imagine your points are in containers. Here is how your account looked on April 26th before you banked.
On April 27, 2018 you banked all 26 of your 2017 points into 2018. Imagine that member services pours the red 2017 points on top of the green 2018 points but they don't mix up. The red 2017 BANKED points sit on top of the green 2018 points. your 2017 container is now empty.
On May 24, 2018 you make a 44 point reservation for April 2019 at BCV with your
DVC points. Member Services uses ALL 26 of the the red banked points first for the reservation since they have that one-way trip into the 2018 UY and they need to be used as soon as possible so you don't lose them. Imagine that member services pours out the points from your 2018 container into your reservation. ALL the 26 red banked points
go in first and then the rest of the reservation is topped off with 18 green 2018 UY points.
This is the current state of your membership. Your 2017 UY container is empty. Your green 2018 UY container has 1 point. Your April 2019 BCV Reservation has 26 red banked points and 18 green 2018 UY points.
ALL of your banked points have been used.
You may bank that 1 green point into 2019. It is not lost.