I dunno if this was meant to be a kneejerk reaction or a smartass comment, but "canon" can be used 1 of 2 diff. ways, "as a descriptor of specific incidents, relationships, or story arcs that take place within the overall canon." So the context I used it in is still technically correct.. the X5 ending in which Zero died "for real," X loses his memory of him & describes Elysium to his comrades isn't considered the "canon" ending. It's not that big a deal, man.. 
It sort of IS a big deal. you have no idea how much the Mega Man fandom misuses the damn word. Throwing it around like its nothing. Not canon are for example, the mangas. they are not canon to the games. or the bandai card series, which is 'semi canon'.
just for the record...
1
a : a regulation or dogma decreed by a church council b : a provision of canon law
2
[Middle English, from Anglo-French, from Late Latin, from Latin, model] : the most solemn and unvarying part of the Mass including the consecration of the bread and wine
3
[Middle English, from Late Latin, from Latin, standard] a : an authoritative list of books accepted as Holy Scripture b : the authentic works of a writer c : a sanctioned or accepted group or body of related works <the canon of great literature>
4
a : an accepted principle or rule b : a criterion or standard of judgment c : a body of principles, rules, standards, or norms
5
[Late Greek kanōn, from Greek, model] : a contrapuntal musical composition in which each successively entering voice presents the initial theme usually transformed in a strictly consistent way
all those endings OCCUR in Mega Man X5, and therefore, they are part of the canon. They are all simply branches into different paths. Paths simply never explored. in one ending, X's memory of Zero is wiped and he mentions wanting to create Elysium. (now mind you BTW, Elysium was the English name for the place, which in Japan was named 'Heaven' so whether he was reffering to the Legends place or to Neo Arcadia is anyone's guess )
And suddenly we have the introduction of Rockman Online, which apparently takes place parallel to the Zero series. Which makes it it's own branch. one branch goes tot he Zero series, whereas another leads to Rockman Online. (that is, if it is to be considered part of the Mega Man canon at all, )
I got the 3000 figure from the fact that The Master survived for about 3000 years, the exact figure could be 3500-4000 years for all we know.
thats how long he has survived for that long, but we dont quite know what happened before that. remember that something had to happen to flood the world and create the elder system that is somehow supressed by the Master system. But master never makes any mention of it in the flashbacks. (maybe Legends 3 will?) Its very possibl that much happened even before the Master. I mean we've got People like Master Albert and Master Thomas who want to reset the world, and in legends, seems very much like that happened. There has been an INCREDIBLE technological regression on Terra. Although at the same time, Carbons are basically advanced partly organic robots.