So we hosted a webinar with GoToWebinar (no problem). The webinar was correctly synced with Marketo, so all of our registration information (attendees, no shows, etc) all correctly recorded into Marketo.
The event was also synced with a SFDC campaign. However, only some of the registration information synced correctly. So, while 38 people attended the webinar (and this is correctly recorded in both G2W and Marketo) only 23 people are listed in SFDC as "attended". The other 15 people are listed as "Invited".
The Marketo smartlist that leads to the "attended" SFDC status change is:
Program Status is Changed
Program IS our.program_name