The Add To Outlook functionality built in to GoToWebinar is dependent on the limitations in Outlook for recurring calendar items. If Outlook does not support the pattern of the additional recurring dates in the calendar file, it will only read the initial date.
Each session must be:
1) Same time of day
2) Same duration
3) The pattern must be the same every week or month
4) Recurring every Wednesday and Friday is fine, but Wednesday this week, Friday next week, and Monday the week after will not work
5) An easy test to see if the pattern you want will be understood is to go to Outlook and create a new empty calendar item and go to recurrence. The patterns there are the ones that Outlook understands. Anything else will not be.