OTOH, if 2283 is to be interpreted as a stardate, we have to accept that 6000 SD units represent some fifteen years of Kirk's life - meaning the stardate system must have "hidden digits", or else stardate zero would have been within Kirk's original mission as well and most of the immediate Trek history would consist of negative stardates. Which doesn't seem to be the case, as we never hear of negative dates, but we do hear of old yet positively stardated events in TOS (such as the background on Kodos).
With hidden digits, Kirk would be left wondering whether the ale is fifteen years old, or a hundred and fifteen... And McCoy would be giving him a somewhat different reply!
I still think it's supposed to be an actual date.
The stardate has never been a system with set rules. In TNG they decided to put it at 1000 per year (explaining away that impulse acceleration accounts for distortion, though that doesn't work for DS9, which uses the same system). I actually like 1000 per year because it's very very different from the current date.
Of course it wouldn't be very practical, and it doesn't fit very well with the stuff from TOS. But if TMP was on stardate 7400, that would put it 18 months after Turnabout Intruder, at stardate 5900. Cycling back to zero after 9999 would put TWOK's 8100 less than 11 years after TMP (which is pretty close to the official dates), and 15 years after Space Seed (3100).