I don't know what it is, but I know it when I see it.
Is bareknuckle sparring (50% to 80% force depending upon rank and experience) realistic enough? Are broken ribs(lots of those), broken hands (mostly from hitting something hard like a guys head, sans headgear, without gloves), dislocated elbows, guys throwing up after getting kicked in the gut, a concussion, a dislocated jaw and yeah, getting knocked out, not to mention the bumps and bruises from landing upon a hardwood floor if you get swept or thrown, good enough for you? Done every class and not once a week or month on a nice mat, real enough?
Guess what, I know it isn't a real situation. Because I know that while we may get "lost in the dance" and do damage to each other, it's still not a street fight. That the fight will end and help given to those that need it.
And one thing I'm laughing at is a JKD guy telling me not to play word games, because the BS the average JKD student runs around spouting is what help turn me off to it in the first place.
I do believe that Inosanto, Vu ( I learned under one of his direct students for a while, very good instructor), Hartsell( grappling before it was cool) and the others you mentioned as knowing what it is. My pokes are at the ones who are clueless and illogical in their definition of JKD. Those who mimick Guro Dan without understanding the mastery the man acheives.
And I'll be honest, I don't know what JKD really is either. I've seen it used as a pure "marketing phrase", a set of concepts, a set of skills called concepts which means that they aren't really concepts, and a martial art unto itself (I'll use the definition of porn, "I don't know what it is, but I know it when I see it"). If any one can describe it, it would be Inosanto. He knew Lee, trained with Lee and was friends with Lee. But even then there would be those who would contradict him.
The reason JKD is so hard to define is that if you define it as an art then it can't be a concept, but the concept of JKD, to me at least, is what really makes it unique.
Adventure is just a romantic name for trouble. It sounds swell when you write about it, but it's hell when you meet it face to face in a dark and lonely place.
Louis L'Amour