It doesn't make sense to me that "I am legend Alternate ending" qualifies as a film of it's own,

I am not sure the alternate ending of I Am Legend should constitute its own film entry, and I strongly suspect it is going to be subject to deletion because

1. TMDb does not currently support different releases of movies
2. The movie does not have its own unique IMDB ID number

I won't delete it just so Travis or another moderator can confirm this.

I put up The Big Sleep 1945, because it is a completely different movie than the 1946 version. I looked for it today and I think it's been removed [...] but not the original cut of The Big Sleep. Can someone explain this to me?

If it was deleted I suspect it may be for the same reasons given above. Does this "original cut" or pre-release version have its own IMDB ID number? I cannot locate one.

Thank you for your reply. No it does not have its own IMDB number. I emailed IMDB over this last night. There is at least one actress who doesn't receive a film credit because of this. Judging from all the student and amateur films that do receive an IMDB number, it seems insane that a film that has been released on VHS and DVD and has been aired many times on television would not.