Worried that an old client can intrude? Don't be!
Only you can let someone into a Session. The video call itself doesn't have a URL; only your waiting room has a URL and even if two of your clients arrive in the waiting room at the same time, they are not able to enter the Session or see each other unless you grant access, to the same Session, for both of them.
When a Client enters your waiting room while you have a session in-progress, you'll be notified and you can grant access if you choose to.