I found the reference -- I remembered wrong. It says: "Wavy coats are visible in Yorkie puppies at a very early age and in general portend a light silver adult. A slight waviness on the upper hindquarters is not unusual in many Yorkies, but should be watched."
Yorkie puppy coat color stages within the first two years of maturity - yorkie hair color
Ben is not a light silver, he is a fairly dark steel blue. But his waviness was slight (I could blow dry it out completely), just on the hips, and left very soon.