A smart field shows that it has been run multiple times in the history however the Last Run On date is not populated.
This means that the results have been cleared for the smart field. Clearing the results of a smart field will clear the last run on so that it can process in its entirety.
Steps to Duplicate
1. Select Smart fields from the Administration functional area 2. View smart field in question 3. Note it has a last run duration but that Last run on is blank 4. Select the smart field 5. Note that the recent status shows this was run