I was told by a FA about a year ago on flight from IAH to LAX that I was a CO*. I bought my ticket last minute after upgrades had happened and was forced to sit in the back of the plane. The FA greeted me at the door of the plane, walked me to my seat, and gave me a free pair of ear-conforming headphones. I assume that this was a CO* amenity. Though my status has not changed since that time, I have not received similar service on trips where I was not upgraded.