The event in question - which the asker has named elsewhere - is a relatively small open road sportive. Much more like a typical audax than a big closed road sportive.
??
He’s just speaking his branes.
I suppose there wouldn't be real problem with crashing a relatively small open road sportive. Such an event would be much like an Audax. There are various events around here that have been run as Audaxes, and as Sportives.
There seems to be a point at which the 'private excursion' bit becomes unconvincing. An interesting point is whether the AUK insurance is valid if you're doing a DIY in a sportive when you're not entered in the sportive.
Anyway, as I said, I can't think of any pressing reason why AUK validation shouldn't be extended to organised events, if there's a demand for it.
I find the likes of 'Chase the Sun', intriguing.
https://www.chasethesun.orgThere was a group at LEL 2017, some of them had done that as preparation. I encountered them at the 24, and asked if they were doing PBP. They said it was a mystifying faff to qualify.