I think the official gilet functions well for the organisation. It's immediately possible to tell who is an 'official' volunteer. One surprise was that the Le Ribay crossing was policed by volunteers from the local community, as they had non-PBP Gilets, and 'Le Ribay PBP 2019' T shirts. They were occasionally augmented by ANEC moto riders.
That was a significant contribution to volunteer organisation. Just imagine working out a rota to police that very dangerous crossing from 'pool' volunteers, for about 60 hours.
There was a big pile of gilets, volunteer T shirts and specialist service armbands at the HQ, tending to suggest a shortfall in volunteers, which was offset by quasi-formal community support.
I wore my 2015 gilet while I was filming next to the Cafe Patton at Meen Le Grand. The route was very well signposted, but many were unsure, and needed directing. The sight of the gilet was a big reassurance. There were others directing; local club members with a rider in the event, but that was very informal.