Here is my recent experience. Purchased BOS-LAS-BOS for December back in August, the pricing was comparable to EML seats at that time. Selected 4A and 4F for wife and me. 2 weeks prior to flight changed to 2A, 2F. 10 hours prior to flight got a lucky message that my seat was broken and I was "proactively" moved to 1A. At that time, three seats were still vacant in Mint. Gate: talked to a GA, was advised that the seat 2F was broken, was also told that 1C was not occupied, so I thought I would be alone anyways. Note that there were several people with no seat assigned and the GA invited them to the gate to get their boarding passes. Boarding: Talked to a FA before taking the 1A, she suggested that 2F does not recline at all. I get to my 1A, a second later a lady takes the 1C and I could see her BP with 1C assigned. I immediately asked the FA to be moved to my original seat, never mind it does not recline. To my surprise, another lady arrived to this seat, brandishing her BP with 2F assigned. We sent her to 1A, and she looked happy with the reclining seat. Bottom line: at least three Mint seats were given to the no-seat-assigned people.
The return flight was uneventful, I saw two vacant Mint seats. My 2F functioned OK and did not seem to be too worn. Interestingly, the return flight had the same FAs and they recognized us. I am not sure though if the plane was the same or not.