Hello, I'm by no means an expert, not sure about ladies wrist-watches, but I believe that some 19th century pocket watch case companies had their own way of describing the thickness of the our layers of gold filled. They used to use terms like, "guaranteed 20 years" or "guaranteed 10 years" in relation to the thickness of the gold sheets. "20 year filled" sounds like it might be a derivation. Just a thought.
