Can you give me some examples using the existing system and what you'dPick August 29th (the next example date) and create an event on it.
o Check Event Repeats
o Select Monthly
o Repeat every 1 Month
o Repeat by day of week
The repeat Summary says "Monthly on the Fifth Wednesday".
My first reaction is to say that's daft. Who wants an event that skips some months? So one possibility is just to change the logic (and that text) to implement "last" instead of "fifth".
But undoubtedly some users do. So the other option is to, in that case, reveal a control (radio buttons) to select between "fifth" and "last", probably just below the control that selects between "day of the week" and "day of the month".