I have found that when I have a nice topline in a pup, rarely (well never) has it went "off". Structure is so very tricky in this breed and it can surely throw us a loop now and then but it has been my experience over the past decade that once a topline settles, it stays. Once a dog reaches adult hood there is no reason for structure to go "on and off" unless there is a health issue.
Good luck to you
