" confirmed the field object was restored to the original size "
Maybe the original size is still not enough. Test this by making the field much wider to be sure. This calc field is based on the first and last name fields in the same table so it doesn't rely on relationships or table names. Even if you changed the field names Filemaker would adjust the calc to reflect the new field names. So the only way you should be getting "?" is if the field isn't big enough.
Apparently it was not the size of the field as I did as you suggested & enlarged the fields, which made no difference however when I created an additional space at the begining of the text. This I did inadvertantly as I corrected a name the last name field in Browse mode, I then found I could view the full name in the Contact List Report....yeh! So many thanks.