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Every now and then I look up something about Game of Thrones (exceedingly tentatively, as I haven’t read the books and am trying to avoid spoilers), and end up on A Wiki of Ice and Fire, a wiki describing the book series, not the TV series.
Often I can spend ages clicking through various pages and not get spoiled, as a lot of the information there seems to describe the distant past of Westeros (and the rest of the world), before the events depicted in the TV show (which, presumably, are the events depicted in the five novels too).
And there’s an enormous amount of stuff there. Each major family that we see in the show/books seems to have a fully-fleshed out dynasty stretching back hundreds or sometimes thousands of years, with descriptions of what each significant member did during their lives — what battles they fought in, how they gained and lost their power, and so on.
Do all of these stories really come from the books? (Presumably from conversations where characters discuss history.) I know the books are pretty hefty, but the history of the world as described by the wiki seems way more fleshed out than would be possible even in five novels.
Are there other sources from which this stuff comes from?