I have a "Master Calendar" that is an aggregate of several different subsite calendars. This works well in SharePoint, but when I sync to Outlook, it only shows events placed directly into the MASTER calendar and not ones from the subsite overlays. Is there a way to sync all of them at once?
The Calendars Overlay feature is used to create a combined calendar view. It does not save the data from other calendars to the current calendar. It is just a combined calendar view. And the Connect to Outlook feature is used to connect the current calendar to the Outlook, not for the view. So that, the other calendars overlaid to the Master calendar will not display in Outlook when connection Master calendar to Outlook.
To achieve this requirement, you need to copy events from other calendars in the subsites to the Master calendar programmatically. Use the event receiver to monitor the item events in calendars in the subsites and then create items in Master calendar.