We had a webinar today and had set the registration limit to 97 attendees. A few hours before the webinar, we went on GoToWebinar and had a notice that registration was full even though there were only 75 registrants at the time. I did a test registration and was able to register myself for the webinar so I figured the notice was just a glitch.
After the webinar I ran a registration report and there were only 87 people registered, included those who had cancelled their registrations.
I don't know if this is related or not, but we were notified after the webinar that one attendee had tried to log in to the webinar but received a message that his registration had been cancelled. He forwarded the reminder email he had received from GoToWebinar 24 hours before the webinar and it had a peculiar subject line. I've attached a screenshot of it.
Sorry to hear about the mixed results you received on your recent GoToWebinar broadcast.
You are technically allowed 10 times the registration limit that you are allowed in a live session, so in your case you should have a 1,000 registration maximum per webinar. However, each scheduled event can also set this maximum lower than the standard default, in the Registration settings area.
Attendees clicking a join link should not receive a 'cancelled' message ever, so that's something I think would be interesting to test further with that particular registrant.