That's interesting. On a recent flight between GRU and ZRH that was overbooked by 1 in C and 11 in M (but had enough capacity in Y to absorb M pax while F was full), I volunteered for denied boarding (I was in C). A gate agent in GRU was happy that I volunteered; however, she had major difficulty to offload me (no luggage, checked in 2,5 hours before) as, according to her "the system kept putting me back to the flight." Eventually, she checked me out and then rebooked. And then the station manager came and said "Ah, HONs and SENs will not even receive a pop up message during OLCI to volunteer and internally, it's a nightmare to offload."

On the other hand, on VIE-BKK that was overbooked by 6 in C and 11 in M, OS duty manager easily offloaded me and offered virtually any rebooking option, including VIE-IAD-NRT-BKK.