I heard the idea a while back that the Max we meet in Fury Road is actually an adult version of The Feral Kid from the second movie. This would explain one thing with Furiosa that doesn't really make sense if all of the movies follow the same Max. Her and Max appear to be about the same age, and if we use the actors then there's only a 2 year difference between them, but in Furiosa we see her as kid in the post apocalyptic Green Place, and in the original movie Max was well into adulthood and the apocalypse appeared to have only recently happened.
Another idea I heard, and for some reason I'm thinking this might have come from someone involved in the movies, is that there is no real Max and the movies are just stories people tell about a mythological figure called "Max". Which could explain some continuity issues like Bruce Spence playing almost identical characters in 2 and Beyond Thunderbome, but Max and his characters meeting for the first time in both movies. It could also explain the drastically different states of society in the different movies.