So in looking for ways to create adventure hooks to explain the various holes in the Ravenloft timeline, I've recently come to Mordenheim and Lamordia. As we know, there is a number of holes where the existence of Lamordia is referenced even before its existence (example: Lumley hiring Vistani to steal the Notes on Animation
Children of the NIght: the Created) and that there have been two given dates for its formation (Domains of Dread gives it as 575 BC as an Island of Terror not joining the Core until 683, whereas Ravenloft 3e gives 683 BC as its formation date. Either way you'll get some continuity efforts)
My solution to the above is that it was
originally 575 BC, but then Mordenheim did something in an attempt to avert his fate. Specifically, the idea hit me from the novel Mordenheim.
In the book, Mordenheim mentions that the previous owner of Schloss Mordenheim, Baron Heimreich, had a library that included tomes on "metaphysics" that he said the Kreuzters were welcome to use since Mordenheim had no use for them. At the end of the Mordenheim novel, the doctor is overtaken by rage at magic and its unreliability. Therefore, in his normally out of character rage, it is not unreasonable to assume he might return to said library and burn whatever tomes were still in said library. However, going through the books, Mordenheim discovers some works on quantum theory and time travel. They are quasi-scientific enough for Mordenheim to translate them into actual (weird) science. So he begins work on a transgression greater than any that came before: instead of playing god with "just" one creation, he would play god with the entire timeline, altering history to change the events of the past.
Of course, things do not go well for him either, in that, beyond things turning out pretty much the same way they did before, there were certain temporal distortions, such as what occurred with the Automatic Man and the Kreuzters unexplained for jump to the future. In the "reboot", Lamordia forms much later, but it still does, just this time it's in the Core. What other ramifications I will leave to you. Perhaps Mordenheim might try again in the modern timeline. Could making for an interesting Time of Unparalled Darkness scenario.