I have always assumed that airlines would not deliberately oversell the premium cabins, for obvious reasons, but just saw some evidence to suggest otherwise. I'm waitlisted for an upgrade to BC on a domestic flight that's showing F0 C6, yet all FC seats are assigned and all but one in BC are taken. I know that two seats in Business are often blocked until T-24 on international flights, but five blocked seats seems unlikely.

Is this really an oversell? Has this sort of thing always been happening and I just never noticed, or perhaps it's a PMCO thing?