That was a tortuous post title! Another post to help me remember.
I created an InfoPath 2013 form to add a new list item. One of the fields was a lookup field using a column from another list.
The lookup field was a Person field, which in InfoPath looks like repeating data.
I needed the dropdown list to show values where there was nothing in this Person field. It took me a bit of messing about to get it right.
The trick is to filter on the group. In my instance, I needed to show all entries where there was nothing in the User field for that list item.
The logic required was “All occurrences of Person are blank”, on the List Item row.
Hope this helps someone…