Thanks Steve, that helped. (Didn't use the correct search phrase when I looked.)
I decided to go with the optional text box and make it a combo box so I could a. make sure it was filled in, and b. provide the date format I wanted used (mm/dd/yyyy).
I would still like to know if imported items, or import changes, trigger the last edited field. I was hoping someone new off the top of their head so I wouldn't have to try it in my sample data (I always make a mistake when I import item changes

).
PS Need some more optional text fields in inventory.