Relevant documentation indeed. Although, ANN must have made a translation error. If Dennou Coil was based on a novel, that would be both surprising and awesome. I mean, if this were true, this would have been common knowledge.
If you believe Wikipedia, then that novel series began one month before the anime first aired. And if you believe Wikipedia again, then the concept was a decade in the making. It’s possible that the first volume of the novel was also a decade in the making, and only the author and production staff knew of its existence, but… I’m just beating a dead horse at this point aren’t I.
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The novel is a side-project which actually has a somewhat different plot and some different characters from the anime. It is like an alternate interpretation of the original concept, but written by someone else under supervision of the original creator Mitsuo Iso. (Incidentally that someone else, Yuko Miyamura – not Asuka’s seiyuu, despite exactly the same name – co-wrote episode 7 or 8 or something of the anime).
The anime was most certainly not based on the novel. The anime, novel and short-lived crappy manga were based off Iso’s original proposal. A recent artbook features it.