I don't know the answers to all of your questions, at least not yet, but the seven fonstones were originally suspended in the fonbelt - it's a ring of seventh fonons that surrounds the planet. Some force must have caused a number of them to fall back to Auldrant, and I imagine they broke up in the atmosphere as a result.

It seems to have something to do with Lorelei, but until I learn more about Lorelei itself, I'm at a bit of a loss.

The Score wasn't always inaccurate. It's been fairly reliable up to a point, and that may be because people are afraid to diverge from what the Score foretells. The world began to fall off track only recently.