Wondering if you have code samples regarding validating different sections of the recurrence editor. For instance if the user selects a daily recurrence then deletes (using keyboard) the value in the "After" spinner or the "On" date/time picker. Or they do something similar with a Weekly recurrence and perhaps check none of "Repeat on" checkboxes and delete values for "After" or "On".
I see there is some reasonable default saved for RecurrenceRule in the database - is that by design as a way to avoid exhaustive validation? I can see this being a difficult ask, but it only takes one user to enter a recurring event incorrectly and it leads to a lot of confusion and questions. Is this a validation rabbit hole best avoided?