The Canon

[William Cloud Hicklin]

But would we be arguing First Age canon if Tolkien had finished and published his Silmarillion?

Well, of course not.

The thing is, we know that T was willing on occasion to contradict published material, and then regularize the change in print: vide Finrod > Finarfin and Inglor > Finrod.

For that matter, even the published "canon" is not necessarily consistent. Were we to take the Lorien chapters alone, Celeborn would clearly be a Danian (Nando by the later system); he had become a Sinda by the time the Appendix was written but the main narrative was never revised to match, and you have to kinda squint to make the retcon look consistent. See also TRGEO version of Celeborn/Galadriel, especially the "ban."