Robert Comsol wrote:
Both Kirk and Khan, humans of Earth, stated audibly in ST II / TWOK that they hadn't seen each other for 15 years. (IIRC there was still another reference in the longer version of the film).
Unfortunately these "15 years" were not reflected in the "Okuda Timeline" so the time figures of Kirk's era
Absolutely. This is by far the biggest credibility killer in the Chronology, but it isn't the only one.
As for the OP, I'd question whether the Okuda timeline was ever
canon. AFAIC, the fact that the Okudas both worked on the production team was not
proof that the Chronology was canon. The Okudas themselves more or less stated as such in the book (and the second edition was quite pleased to point out that First Contact flatly contradicted their own version of the first warp flight as theorized in the first edition), and with virtually every entry prefaced with the word 'Conjecture', I think it's fair to say that the 'canonicity of the Okuda timeline', if any
, is up the individual reader.
I loved the Chronology and would welcome a third edition that covers the entire prime timeline now that it's more or less a closed book (for now). But I'd never have ever called it a "go to" text for canon.