Hello Susan, Yes there is a way. However, this is a complicated JS intensive thing, and has to be properly managed.
First, the main list has to be stored somewhere global. Then you need a document level function that is called each time a selection is made. The purpose of the function is to go over every list and collect all the selections, Then make a copy of the main list that does not include the current selections. Then apply this copy to each of the dropdowns.
Thank you, it sounds a bit more complicated than I was expecting.
It's complicated because it involves more than one field. but the concept is very simple.
** On the Commit Event
1. Get all selected values
2. Remove from Master List of items
3. Set each field to modified item list