As a feral dps who was third tank in WotLK, I respecced several times every raid. Sometimes for bosses and sometimes for trash.
There were healers who did the same.
There were DPSers who respec’d between trash and bosses.
There were DKs tanks who switched specs to tank certain bosses/adds.
All in all, there was at least one and usually several players respecing EVERY single boss fight.
If you weren’t there, stop guessing.