(Not to mention that it wouldn't begin to explain all the other Klingons walking around in "Trouble With Tribbles" who weren't undercover, who we know from DS9 did in fact look human-like.)
Augment virus.
Well, yeah, that was my point. The Augment virus would explain them nice-and-easy. Retcon that away, though, as MM clearly wants to do, and they remain unexplained.
Memory Alpha has a whole section on the movie's article about how to date the movie
here and there are reasons to use the 2285 date.
Yeah, I'm unconvinced. To quote it...
The film alone does not clearly identify the year it is set on, other than that it is somewhere in the early to mid
2280s. Based on some of the film's dialogue, the film was set fifteen years after "
Space Seed". Khan: "
...marooned here fifteen years ago by Captain James T. Kirk." According to a line in the script, it was more accurately fourteen years after the episode. Kirk: "
He wants to kill me for passing sentence on him fourteen years ago."
[9] "Space Seed" in turn aired in
1967 and is considered to be set in
2267. This suggests
The Wrath of Khan would be set in
2281 or
2282. Nick Meyer's commentary on the special edition DVD, explains that the intention was that the film depicted Kirk's 49th birthday. Kirk was born in
2233, so this would support the year 2282.
Other accounts within and after the film suggest the events of the film took place later in the 2280s. The label on the bottle of
Romulan ale that McCoy gives to Kirk as a birthday gift reads
2283. In
Star Trek Generations, in the
Nexus, Kirk imagines himself eleven and nine years into the past, to the years 2282, when he met
Antonia, and
2284, to the day he told her he was returning to Starfleet. All those accounts suggest the events of this film occurred afterward, as Kirk was at the beginning of the film supervising command-track cadets at Starfleet Academy as an active Starfleet admiral. According to
StarTrek.com,
Star Trek Chronology, and
Star Trek Encyclopedia, (3rd ed., p. 691) the events of
The Wrath of Khan in fact occurred one year later in
2285. Memory Alpha uses this year as well.
From the top: first of all, the film doesn't actually identify its date even as precisely as the decade; it merely says "In the 23rd century." Placing it in the 2280s is an after-the-fact inference that was only possible once the TNG episode "Neutral Zone" (six years later) used the Gregorian date "2364," and pretty much everything else in Trek got backdated from that.
Second, yes, the film's dialogue (from both Khan and Kirk, both of whom were from Earth and familiar with Earth years) did say fifteen years; anything contrary in the script was evidently cut out.
Third, "Space Seed" is only "considered to be set in 2267" by the arbitrary convention (first used in the
ST Chronology) that TOS episodes are set exactly 300 years after broadcast. However, given that TOS episodes almost never refer to one another (and especially given the absence of Chekov during the first season, when "SS" was broadcast!), it would be ridiculously easy to move "SS" as necessary to just about any point within the FYM to keep it 15 years before
TWOK.
Fourth (just as a side note), it's interesting to read that Nick Meyer intended Kirk's birthday to be his 49th. (Presumably he was adding 15 to the "34 years old" line from "The Deadly Years"?) For my part, given the way the TWOK story came across on screen, I always assumed it was his 50th, much more of a milestone of the kind that would get him reflecting on his age.
Fifth, yes, the bottle of Romulan Ale does have the date "2283," but it was never clear that this was a Gregorian date (presumably Romulans bottled the stuff, after all), nor what exactly the implications of the joke were meant to be. It's ambiguous.
Sixth, Kirk's flashbacks in
ST:GEN were indeed set eleven and nine years into his past, but they didn't actually provide Gregorian dates as implied here. Those are inferences based on setting the movie in 2371, which is itself an inference based on its stardate (48632), which would be during the nonexistent "eighth season" of TNG and is typically interpreted as 2371, based on the
ST Chronology's (again arbitrary) convention of assuming that 1000 stardate units in TNG correspond exactly with one calendar year — an assumption never verified on screen and often implicitly contradicted. (E.g., "Data's Day.")
Seventh, even if we do accept 2371 (and hence 2293 for the Kirk opening sequence 78 years earlier, and hence 2282 and 2284 for his Antonia flashbacks), the film doesn't actually give us enough information to place those flashbacks relative to the rest of his career or events from other movies. It's just the day he met her and the day he left her, that's all. It would be an equally reasonable inference to imagine that he considered retiring after the events of
STIII and
STIV (including the destruction of the
Enterprise), and only decided to return in order to take command of the newly christened
Enterprise-A, which after all was basically a gift to him from Starfleet.
Long story short (too late?

), the only hard-and-fast chronological relationships between TOS episodes and original-crew movies are (A)
TWOK happens fifteen years after "Space Seed," and (B)
STV:TFF happens at least 20 years after the end of season one (since the Nimbus III colony could not logically have been established until after the Romulans were back on the scene in "Balance of Terror,"
and the Klingons had been reigned in by the Organian peace treaty in "Errand of Mercy"). It has always struck me as quixotic to disregard one of those relationships for the sake of otherwise completely arbitrary dating conventions and far more ambiguous evidence. FWIW, in my own timeline (headcanon of course, but very detailed) I place these two films in 2283 and 2287 respectively, with a significant time gap between movies 4 and 5.