Would this work if the event was initially scheduled when the “Last”No, then you get the fourth. To be shown my proposed option you'd need to start by creating the event on a fifth/last date.
I hadn't thought of it, but the idea could easily be extended to incorporate the fourth, simply by showing an option to select between fourth and last if the date happens to be a fourth. That way you're covered.
It just seems like the existing algorithm was designed for 28 dayI don't know that there's a mindset issue involved. One benefit of the current scheme is that you can't create a logical problem by defining a repeat that doesn't include the start date (the date on which you created the event).
I'm not sure what the proper interaction is between choosing "fifth" and also a "Repeat Every" greater than one. The current behavior seems to be an intersection of the two (every nth month, unless there isn't a fifth that month). That's probably a sane choice.