Nothing that I can point to as absolute truth but...
I have to fly for work on Tuesday.
I always try to use my frequent flyer status to upgrade to first class seats.
A week ago when I tried to do this, the plane on the flight I was taking was mostly full and no first class seats were available.
Today, just now, I confirmed a first class upgrade, and went to pick my seat online.
The plane's seat assignment chart showed it nearly 3/4 empty.