Yes, this is according to not only my breeder, but other breeders as well. Here is one bit of info from a prominent judge and breeder:
Originally Posted by kmatt
Cavalier bites can change up to three years of age; it is very frustrating for the breeder to see a good mouth go off and a undershot mouth correct itself in the most beautiful, neutered Cavalier in a pet home. Don't fault mouths too much in a puppy as the bite may change daily, but the scissors bite is ideal and is strongly encouraged; undershot is strongly discouraged. The standard calls for a scissors bite in a Cavalier. At this point a
level bite is not considered a fault. Overshot
mouths, including a parrot mouth, are very faulty and
should not be rewarded.