I got to implement recurring meetings in a web-based calender app a few years ago. There were several gotchas that got re-done a few times. Deleting partway through the series was one of them. I do remember explicitly providing the option to delete a single event, or deleting from this point forward - I don't think the app permitted past events to be deleted.

Sidenote: the database structure got a little curly to support editing a series, as well as individual entry.