CO has the BEST (worst if youre LOOKING for a bump) rev. mngt team out there!
It is soooo rare to see a plane with an open seat, but also i almost NEVER hear offers for VDB.
Last year I had ~180+ CO flights, and had the opportunity ~4 times, and took it ONCE. Did have F oversold ~2 times, and all they offered was a "space available F class u/g" to "give to a friend, etc".