They design changed in every TOS era film in which they appeared, TNG where Klingon women finally got the same level of ridges as the men, “Into Darkness”, Disco twice, and now the most recent episode of SNW. Some of the changes are more subtle than others, but that doesn’t mean they weren’t changes. If the bonehawk Klingons from TMP showed up in TNG, you wouldn’t automatically assume they were Klingons.
As for the augment virus in ENT, it is actually an extremely poor explanation which doesn’t account for things like the Excalbian recreation of Kahless appearing in “The Savage Curtain”, or the fact that Kor, Kang, and Koloth are all in both TOS and DS9 looking appropriate for their era. Fortunately ENT never flat out says the augment virus is the reason for the different appearances, so it can be safely ignored so far as this conversation goes.