Dylan is having fantasies about what his future would be like with Kelly and Brenda. When he's fantasizing about Kelly, he gives her a piece of jewelry bearing an emerald, at which point she gets angry and says, "That's Brenda Walsh's birthstone. You're still carrying a torch for her, aren't you?" However, in Parental Guidance Recommended, Dylan's mother talks with Brenda and makes reference to the fact that Brenda's sign is Scorpio. Scorpios are born between October 22 and November 21 (give or take a day), but emerald is the birthstone of May. Therefore, there is no way that Brenda's birthstone could be an emerald if she were a Scorpio.