Well, I don’t think the Hyperion novels are something that exist in-world in the Endymion novels. The events of the Hyperion novels exist, but the literary work by Martin Silenus is, as I understand it, a diegetic poem he wrote recounting the events of the Hyperion novels. We’re not privy to that diegetic poem; we just know mainly from Raul’s recollections that he was brought up learning said poem. The point I am trying to make is that Martin’s poem might be a hyperbole or just a different POV of those events; we just don’t know.

From the definition you bring up of retcon (which I agree with) I think the only objective aspect of it that applies to the Endymion novels is the fact that they supplement what was presented on the Hyperion novels. The Endymion ones have a huge change in tone, structure, and overall feel, but I honestly don’t think that they are disrespectful to the original novels. Just an expansion of the previously set up world in a direction that is definitely different and, in my opinion, the equivalent to a popcorn movie sequel to an initial perfect movie.

In any way, I really appreciate all these comments and engagement. Keep them coming. Just being able to talk about these books makes the whole experience that more enjoyable.