The events being TNG’s portrayal of Klingon culture being at odds with the way it was depicted in the novel, with its language, klingonaase, customs, ranks, social structure and so on.

But until that came along, a lot of it was taken as if not official canon, then fan headcanon, like the existence of human-Klingon fusions to explain the ridgeless Klingons, the history of Klingon-Federation relations and so forth. Ford wrote material expanding on the novel for the FASA role playing game and it became part of the fan lore for quite a while.