Is there any elegant way to differentiate between dates that are added (as dates with events on them) to the weekly selector click?

I have an events diary that marks all dates with bookings, but I also want to allow my users to use the weekly select function to add events that span the entire week.

So far I have only come up with a crude method of counting character length, then isolating the last x number of characters the select function adds.

There must be a better way..?

SFO

I have an array of dates already added to the Calendar's SelectedDates collection. What I am asking is there any elegant way of separating out those dates already added to the new dates that are added when I click the weekly select characters.