Here's the response I got from the author of "Guy Williams: Behind the Mask"-
HI
I listened to this after reading your email and I know exactly what you are talking about. Very astute of you. I became curious and referenced Gerry Dooley's book, The Zorro Television Companion. Gerry is seen on Disk 6 in the bonus interviews. We collaborated on our books. On page 54 of his book he says:
"The opening theme also contains a brief instrumental break which was eliminated in subsequent episodes."
Before this he states that the first episode was announced by Dick Tufeld and the silhouette of a fox apperars on a wall, and Zorro appears in the shadow with his cape obsuring the lower part of his face. (Have you ever seen this opening? It's pretty neat.) Gerry's book is great, with lots of info about each episode as well as information about the making of the show and brief bio of Guy's life. When you read his notes before watching an episode it enriches the experience. "
So she came to the same conclusion I did from the Dooley book and gushes over it, too.
Perhaps, I shall purchase her book next.