I don't think Verad was forgotton so much as he wasn't necessary. After all, Verad was only in the body for a couple of hours. There isn't a lot Jadzia needed to learn about him to better understand herself. Joran was a Dax for several months, wasn't he? And I think "Invasive Procedures" deserves a lot of credit. Since I missed the Circle Trilogy, it was the first season 2 episode I saw, and it immediately got me interested in the show again after season 1 left me wondering if I should bother continuing with it.