"We reserve the right to surprise", page-6

My understanding it happens the other way around.

Exerpt on some important bits of PRV's

Priority review vouchers do not expire. Furthermore, the priority review voucher program for neglected diseases (enacted in 2007) does not sunset. However, the program for rare, pediatric diseases will expire in October 2020, although a drug designated as a rare pediatric treatment can still receive a voucher if the drug is approved by October 2022. Furthermore, the program can be renewed, and Congress has renewed the program several times already.

Happy to be schooled if my understanding is incorrect.