I had a rider thank me for a film I made, at the end of the ride at Loughton. It was the 'LEL Cushion' one.
That was based on the conventional approach to PBP; 'Fast out, tour back'. That derives from the usual PBP Westerly, and works because you need to expend more effort into the headwind, in anticipation of a tailwind on the return. PBP 2011 had tailwind both ways, so lots of finishers.
LEL is more 'Make hay while the sun shines'. There's every chance of a tailwind on the way up, and a headwind on the way back. The message that intermediate control times would be subject to some latitude made sense in order to limit demand for beds. However, it removed the spur to make progress in the first half. PBP does that by making the out and back asymmetric in time terms, and adhering to control time discipline.
I got the impression that slower riders thought they'd be able to make time up on the return. That may have been based on PBP 2015 experience. But anyone who knows Britain, knows that the chances of a Northerly in August is remote.
There were plenty of finishers without Audax experience. But they were young, strong, keen, and had exercised due diligence in their research.