Sure it's tough to define, but if we take it to be the actual events that occurred, then we don't have to worry about referring to it as what any given set of people remember or choose to set forth. Obviously if that's what we take it to be, then it is unalterable.
.......So you agree that none of your claims are supported...?
I don't consider pictures of Michael Phelps evidence. Again, show me 10 million successful, frequent potheads, and I'll find you 10 million unsuccessful potheads; the data that is lacking is that did pot make people successful or not, or did it really not make much of a difference. It's a mind altering substance, much like booze, and causes people to do things differently then they would have if not under the influence (to use a cliche).
.......So you agree that none of your claims are supported...?