I have been SheerID verified with Princess for years. It should be on my account and apply automatically any time I book, but it never has. I always end up needing to email the military benefit mailbox to get it, and they respond very quickly and apply it. One time I forgot to check before leaving for the cruise, but Guest Services was able to get it applied for me within a day.
The email address is militarybenefit at princesscruises dot com. I submit an email with my Captain's Circle #, Booking # and sail date, and state that I'm already SheerID verified.