But that doesn't add up!
It's either has enough headroom, in that you can get to the volume you need without the signal being altered, or or it isn't, in that by the time it is loud enough it is altering the signal. The point on the dial is irrelevant- so many factors in how a rig as a system can be topped out, could be the power section, could be the speaker/s, could even be the room.