Sure, but that's not really a complaint that was brought up here. This conversation has been free of complaints about lore and instead just interesting discussions on reconciling it.

I remember a specific moment at the end of CR Campaign 1 where the party was battling Vecna, and Matt made the players make an intelligence check when it looked like Vecna was on the ropes and about to be killed... the players were attempting a complicated process of sealing Vecna away, but were very close to simply depleting his HP. With a successful INT check, the players realized this wasn't literally Vecna, but his avatar, and if his avatar was destroyed Vecna's true form would be weakened, but he could simply return in a few years to wreak havoc once again. 

So I take it to mean that Vecna can manifest in multiple avatars when the opportunity arises. It even lends to the idea that there can potentially be multiple hands/eyes of vecna (I mean, aside from the two of each he starts with).

Quote from PenelopeTheWeaver >>

Right! I was thinking of Lolth. In Lolth’s case I think she began in the Feywild because that’s the home plane of the elves and spread to other spheres/ planes from there. (Or did they change that in MToF?) Vecna probably started on Oerth (where he was a regular lich  who became a god) and then later expanded to other worlds like Toril and Exandria.

 Trust MToF to change everything, but I've gone into that elsewhere. At least in FR (I can't really speak for the other settings), Lolth was originally part of the Seldarine (elven pantheon), and she turned against them, abetted by Vhaeraun and some other evil deities. Her original home was in Arvandor, but she was cast out. The elves themselves originally hailed from Faerie (later called the Feywild). 

My thought (and this is just a fan theory, but similar things have been discussed in forums like Candlekeep) is that multi-spheric deities such as Lolth are all part of the same entity, but in each setting, they develop their own personalities and histories (for example, in several settings, Lolth is the evil spider queen goddess of the drow, but her lore is a little different for each setting). Each "Lolth" comes from the same Lolth, but is also an individual goddess in each setting. Kind of like a deity sending out a bunch of avatars, but of course, in this case, it is also a deity in and of itself. 

Quote from Davedamon >>

I mean, it's known that Matt Mercer borrowed Vecna for his Exandria campaign, which like you said, a lot of people do.

However, a lot of people also enjoy doing deep dives into lore and canon, and with Matt's setting being brought into canon, it's fun to try and fan theory a reconciliation for what that means. Sure, you can handwave it away with "it's just conflicting lore, it doesn't matter, ignore it" and that's valid for a lot of people who aren't into lore and canon. I know for a fact the concept of canon is a contentious one in D&D, even more so than in other fandoms. But ultimately that's just kind of dismissing what people enjoy and doesn't really bring anything to the table as far as the conversation goes.

 Thank you! So much this! While canon is indeed contentious, a lot of people are here for the lore as much as they are anything else, and I know a lot of people try and reconcile inconsistences and tie them together. Discussing canon (contentious though it is) is part of the experience for many. 

Quote from Davedamon >>

Sure, but that's not really a complaint that was brought up here. This conversation has been free of complaints about lore and instead just interesting discussions on reconciling it.

 Reconciling lore is cool 😊

Wait. What if a character obtained both the Eye of Vecna and the Hand of Vecna? Would it summon Vecna or would Vecna possess that character?

Quote from Third_Sundering >>

Quote from DRAGOLICH12 >>

Where is the eye of Vecna specifically in FR lore?

Unclear. In Critical Role, I believe it was destroyed (correct me if I'm wrong), so it may not exist anymore. 

 
I'm not anywhere near up to date on CR lore, but generally, artifacts in D&D cannot be truly "Destroyed" unless very specific criteria are met. The existence of the Hand of Vecna with Arkhan the cruel implies that the condition to destroy the eye has not been met yet, so it must still be out there. The exact specifics on this vary. My personal interpretation is that sufficiently powerful artifacts once destroyed incorrectly manifest somewhere else in the universe, waiting to be found. That is unless Matt Mercer has homebrewed his own rules for it's destruction ofcourse. In fact, the hand and eye specify my interpretation to be correct in their default canon:

"Any other attempt to destroy the eye or hand seems to work, but the artifact reappears in one of Vecna’s many hidden vaults, where it waits to be rediscovered."

More generally though, although there is some implications for a loose connection of the canon between Xandria & other D&D worlds, I wouldn't consider it to imply the canon of both are linked strongly enough that an item's destruction or a god's ascendance in one has any baring on it's status in the other. Arkhan the cruel appearing in multiple parallel universes in possession of the hand can just be considered a very unlikely cosmic coincidence...

But, COULD a god from D&D possess someone via their holy objects? So could Vecna possess someone who has both the Eye of Vecna and the Hand of Vecna?

Quote from RangerTwoBlades >>

But, COULD a god from D&D possess someone via their holy objects? So could Vecna possess someone who has both the Eye of Vecna and the Hand of Vecna?

 Yes. Vecna could.

That makes sense. The Eye give Vecna access to the target's brain, and the Hand to the body. 

Just to clarify, we don't really see the eye destroyed.  The party gives the eye physically to Pelor while in his domain and the god does... Something....

Maybe Pelor just banishes the Eye to Ravenloft.