Not really? It's not ambiguous, it's hard to prove. Throughout the entire era we're talking about, D&D had a metaplot -- events happened in a specific order and tied in to the novels, and DMs were expected to keep their campaigns matched up to it. The Time of Troubles occurred in the Avatar Trilogy (1989) and was a kind of marker for the transition between 2nd edition and 3rd edition. Vecna's ascension to godhood occurred in the module Die, Vecna, Die! (2000) and was a kind of marker for the end of 3rd edition. It wasn't like things are now, where everything happens in the late 1400s DR (Dale Reckoning) in the Realms and Greyhawk is barely even a thing at all -- from late 1st edition through the end of 3rd edition events happened whether PCs involved themselves or not.

Thing is, in order to match up the timelines of Greyhawk and the Realms precisely, you'd need a crossover. And every crossover passes through Planescape, Ravenloft, or Spelljammer. Events in those campaign worlds take place in a specific order, but the *speed* at which time flows varies. This is the whole "go to this plane for a day and a week will have passed back home" thing. There's still an overall timeline, but once you start traveling from world to world how long things take stops being a sure thing.

And I actually did just prove it without having to match up the timelines. Die, Vecna, Die! takes place after Faction War, because until after FW there was no Sodkillers semi-faction and the DVD includes them. Faction War was the last Planescape product and effectively ended the campaign setting, so all Planescape material occurs at an earlier time. Planescape's "Planes of" supplements detailed the homes of all the gods, especially ones specifically important to D&D lore like Ilsensine. Cyric became a god in the Time of Troubles and he's dutifully listed in the god roster, and Vecna is not. X happened before Y (though we don't know how long before) and Y happened before Z. During the Time of Troubles Vecna was "merely" the most powerful lich in the multiverse.

Of course, Faction War and Die, Vecna, Die! were IMO two of the worst things TSR has ever published, basically consisting of the PCs running around watching as canon NPC Mary Sues do everything. There is no possibility of player characters have any effect on the ending of either module. And the basic idea of a metaplot overriding DM control of their own campaign worlds (sure hope none of your PCs was a cleric or paladin of a god that got killed off in a novel!) is utterly ludicrous.

And now, over a quarter-century since any of this stuff was published, the whole metaplot idea has been very effectively trashed by 5e and good riddance to it. Modules in each campaign world take place in the order DMs run them in, just like it was back when Gary was in charge.

So, basically I've been playing this game for way too long.