Agnes Molnar has your answer.

http://www.itunity.com/article/filter-empty-values-search-693

For example, I wanted to exclude all expired items without excluding items that have no expiration date.

So based on the referenced example, I added:

-ExpirationTime:1900-01-01..{Today-1}

So any result that does have an expiration date, and whose expiration date is less than today, does not get returned.

Agnes Molnar has your answer.

http://www.itunity.com/article/filter-empty-values-search-693

For example, I wanted to exclude all expired items without excluding items that have no expiration date.

So based on the referenced example, I added:

-ExpirationTime:1900-01-01..{Today-1}

So any result that does have an expiration date, and whose expiration date is less than today, does not get returned.