Thank you so much for that information, Miruna! 
I ended up using the "_Is Set" values as recommended to fill the ConfirmedEvent1 and ConfirmedEvent2 tokens.
The first chronological event will only ever fill the ConfirmedEvent1 token, so I used a Conditional Sequence. If the first chronological event's checkbox was checked, then fill the ConfirmedEvent1 token with the date & name of the event:

For every other event, I started with a Conditional Sequence to determine if their checkboxes were checked, then I nested a Conditional Decision inside. If ConfirmedEvent1 was empty, then fill the ConfirmedEvent1 token with the date & name of the event. If ConfirmedEvent1 was NOT empty and ConfirmedEvent2 WAS empty, fill the ConfirmedEvent2 token with the date & name of the event.
