But it only ever implied that, and meanwhile we had other evidence that implied a separate conclusion, in the form of Kor, Kang, and Koloth.
Which is more likely-- that every Klingon Kirk encountered during his five-year mission was a survivor of the augment virus (edit: Including Kahless, who lived and died centuries before Archer!) and no Klingon encountered outside of that time period was; or that the Klingons ruthlessly quarantined or even executed carriers of the augment virus and wiped it out before it got too far, and TOS’s visuals aren’t literal?