Solmyr did not make Gavin Magnus immortal; when Magnus became immortal, Solmyr was still trapped in a bottle. The Great Vizier's immortality was caused by a spell he created, which had an unexpected effect. Crag Hack is certainly important, but instead of him, they could have featured Ultimate Adventurers (the Terran counterpart of Crag). He doesn't appear in Might and Magic, only in Heroes 1-4. Sandro from Ashan seems to be either the same Sandro from Enroth or has no connection to either the latter or the Xinian one.

I remember that we, you and I, XEL, never finished arguing about what to call the world of Heroes 1-3 and Sword and Sorcery 6-8.

Let's finish it: the world of Might and Magic 6-8 is called Enroth. This is stated in the manual of the sixth part (the phrase "world of Enroth" is used repeatedly, which translates to "the world of Enroth"). Also, Melian, the Guardian of the Planet, is introduced in the sixth part as the Guardian of Enroth. In Might and Magic VII (where spells of the Dark Magic school are described as "some of the most powerful on Enroth") and Sword of Dragons (where Sandro uses "Enroth" as a general name for the world in a conversation with Crag Hack), the world is also called Enroth. In Might and Magic VIII, this name for the planet also appears: in the manual (where Enroth is mentioned as a world, and the phrase "save Enroth from planetary extinction" is used) and by Xantor (who says that "more and more evidence points that Enroth is not the only place with life on it"). Thus, there is more than enough evidence about the name of the world, starting with Might and Magic VI. A few words about the myth that was common in the early 2000s, that this planet is Xinian after the Reunification. This misconception originated from an article by one of the journalists from Igromania (if I'm not mistaken, he was even registered here under the nickname Katrine) about Might and Magic VI-VIII. There are many assumptions and errors in it, caused by an incomplete knowledge of the plot of the games and the history of the game world. For example, CRON is inexplicably called the homeland of the Ancients. In the canonical games, there is not a single fact that would indicate that the planet on which Might and Magic VI-VIII and Heroes of Might and Magic I-III take place is Xinian. The seventh game completely refutes this version: Ultimate Adventurers (the main characters of Might and Magic III), who flew to Xinian but thought that Korak and Sheltem had crashed and went to search for the Ancients in space, speak of Xinian (which they saw) as a different planet in relation to Enroth.