It really depends. I think you are referring to "thumbprints" located right on the forehead and on the sides of the head toward the ears. Usually most puppies have this and they clear within the first year however some take longer and others never clear.
With the new standard, an adult dog *can* be disqualified for thumbprints.
Sometimes thumbprints are an indication of coat texture--maybe more experienced breeders can comment on this. From my experience I have seen many soft coated dogs retain their thumbprints indefinitely.
Are you thinking of getting into showing?
As a side note, beware of anyone saying they "breed for temperament" as an excuse for lack of breed conformation (unless they have a LONG line of obedience titled dogs in Utility). At dog shows, a big part of judging the breed is not only the dogs appearance but how well its temperament also conforms. Yorkies are terriers...they are feisty, little busy-bodies who love to dig, chase bugs and run-a-muck. It still amazes me to this day they have the patience to be groomed
