The case of the missing button:) Anyone know what controls whether the + button to add new is visible sometimes and sometimes not?

Check the list creation permissions

Thanks Stuart! I think you're on the right path. The custom field is actually a list/record to the ENTITY. I add a filter to only show type=other name. Since employee, customer, vendor, etc are all considered an ENTITY, and the user role cannot create those records, my thought is the UI forms know to show/hide the +. I'd welcome any ideas! Not a show stopper.

Yeah, if they can't create a new one, the + won't show.

This is based on permission for that role. Each entity has a different permission set. There's a helpful spreadsheet with the FULL list of all permissions in NetSuite so you can see what each permission level can and can't do. Just be careful that the list you download isn't from several years ago.