This is absolutely the case and has been said many times, APs are fixed at the point of order, including these changes.
This is why I got messed up elsewhere with the corporate arrangement between Motability Operations and HMRC and the timings of the impact of the changes on customers.
As customers we are in a protected situation where the time of order fixes a lot of things that are less certain in the corporate world.
I'm Autistic, if I say something you find offensive, please let me know, I can guarantee it was unintentional.
I'll try to give my honest opinion but am always open to learning.
Mark