I have actually done quite a bit of research on the subject of 420, and, like the OP said, its original origin is not really known. There are alot of different variations. One is that The Greatful Dead coined it, or that there is a passage in the bible (verse 4 line 20) that describes the marijuana plant. I would like to believe both of these, but they have been proven untrue. The one explination that I have heard makes the most sense to me. If you know anything about the history of LSD then you know that the creator, Dr. Albert Hoffman, and his assitant were the first humans to ever take acid for recreational purposes on a day that became infamouse as Bicycle Day. The story is that at 4:20 PM Dr. Hoffman and his assistant dosed an amount of acid, that by todays standards, is ludicrous, and spent the day riding around on their bicycles, and as a tribute to that monumentous occasion peple everywhere light up in honor of the father of LSD.

I dont think the origin of 420 will ever truly be found out, people will always tell different stories, and maybe thats what makes 420 so special.


Edit: I also know that the prop 420 story is a urban legend. I know in CA its prop 215. I may be wrong though.