Monthly recurrence lacks day of a certain week option
Most calendars allow for scheduling monthly meetings in two ways. The date of the month e.g. the 5th. The other for the day and week of the month, e.g. every 3rd Tuesday.
Gnome-Calendar lacks this latter option, which I dare say is more common for organizations that plan meetings on a monthly basis. Nearly all my meetings are planned either monthly or semi-monthly in this way. Currently Evolution offers this planning option, but gnome-calendar does not.