The sessions in pubs are not part of the festival itself. They are 'fringe' events. Now this doesn't mean that they are any less important than the 'official' events but rather that they are organised ad hoc by people who, for whatever reasons, do not buy season tickets.

All the sessions I was at had a significant number of players at them with tickets hanging round their necks. But that was only instrumental sessions. Are you saying singers operate differently?