Joseph Porta wrote:Which of the two is it? Or is both possible
Both. And more.
Contrary to popular belief, the background in
40k is not a consistent collection of facts, but rather a multitude of opinions and interpretations - in the past at times explained by Codex authors and novel writers as everything you read being tainted by legend and myth or propaganda. Even the 6E rulebook briefly addresses this in the disclaimer preceding the timeline when it mentions historical revisionism.
Here are a few statements on this subject.
Ultimately it is up to you. You can go either for
GW's minis, or the novel, or come up with something else entirely!