Repeated Events - Ex: Last Saturday of the Month

I tried to add an event that takes place on the last Saturday of each month. Knack interpreted it as the 4th Saturday because of the start date. Some months of 5 Saturdays so the event is not listed on the last Saturday, instead listed on the 4th Saturday.

My understanding is that it is impossible at this point. This would be valuable to me and I am sure many others.