Are crossover events canon?

[Cilia]

Long story short: yes and no.

Within the context of its own game world, crossover events are typically considered canon. For instance, how Lightning, Shantotto, and Iroha made it over to Eorzea is explained - Lightning is just an astral projection sent by Bhunivelze to prepare her for her role of "savior" in LR:XIII, Shantotto stumbled into Eorzea using a spell (the same one that kicked off A Shantotto Ascension), and Iroha was sent by one of the Vana'deilian mothercrystals (or something). Gilgamesh, being an interdimensional hopper, just kinda shows up and it's accepted because he's Gilgamesh.

At the same time, don't expect said crossovers to be referenced in their "home" game. Lightning makes no mention of her time in Eorzea, for instance, and while the female Miqo'te starting outfit is available for her as a garb it's meant to be from a fairy tale (or something). Shantotto and Iroha make no reference to their time in Eorzea in XI; Shantotto because she hasn't been in new content for some time, and Iroha precisely because she's brand new for Vana'deil Rhapsodies. Gilgamesh, again, is just who he is and everyone accepts it; at least he's seeking spears in addition to swords now.

So basically, it's canon within the context of its own game, and if the devs say so. Especially important in XIV.

[KylePearlsand]

Snip

You could argue this is where Iroha's story ends since Hydaelyn did not allow her to return to Vana'diel.

[Cilia]

Shatotto was the one who first devised the method which was the basis for Black Magic. She is basically the originator of Mhachi Black magic.

Ah, well I meant the royal "we."

Just kidding. I did forget that Shatotto was the original owner of the BLM soulstone. Didn't know the rest, though. Considering I'm more of a Dork Kn- err, Dark Knight fanbo- err, Dark Knight, while I did find the THM quest intriguing I've not finished it and focus more on my "Main Class." Since I reached the apex of what I can do as a solo player long ago, I've started playing other classes - maxed SMN, MCH, and NIN. Really need to get back into crafting, but I hate the excessive quantity of items you need now.

Digression aside, Shatotto and Shantotto are not the same.

You could argue this is where Iroha's story ends since Hydaelyn did not allow her to return to Vana'diel.

Maybe. Iroha is quite unique in that she's never sent back to Vana'diel and thus stuck in Eorzea. So she could show up later. Popular theory is that she's going to be the one who introduces us to SAM, but I'm not quite sold on that yet.