One of the sad consequences of this is that some recurrence patterns for calendar events which can be created in EWS are impossible to create in Graph.
What does this have to do with the price of tea in San Francisco?
We're in the business of migrating calendars.
When the recurrence pattern isn't something we can re-create we get testy.
We insert in the standard format, hoping that when Microsoft Graph gets its act together to deliver something like this we're going to be seamlessly running. Even though the results are a little weird on insert you can correct them by opening the series and re-setting in Outlook.
But we do make it easy to find these.
We tag problem recurrences with "ZimbraRecurrencePatternNotMigrated" (this is configurable on a server-basis). So you can readily find them.
You can easily sort them all together in Calendar List view:
Note that in the above example we have the category "ZimbraMeetingsYouOrganize" (yes, the names are configurable on a per-migration basis) to help you find meetings you organize and re-propose them. Our full-state migration process makes this step unnecessary. But full-state is also more expensive.