Here is just another anecdote on the stardate issue I feel worthwhile mentioning.
When German television bought 40 episodes of TOS and dubbed these into German, the introduction narrator said "In the year 2200" and the log entries where "Computer Log # 1 of the Starship Enterprise". Whether this was artistic license or the consideration of something previously unheard of, I don't know.
However, if we were to believe that stardate entries had been made on different logs this would yield a rather remarkable result:
stardate (0)3141.9 "Space Seed"
stardate (1)8130.3 "The Wrath of Khan"
If we were to assume that by TMP one solar year equals 1,000 stardate digits, the elapsed time between "Space Seed" and TWOK would amount to 14,988.4 stardate digits.
I'd say 14.99 years is definitely close to the 15 years mentioned by Kirk and Khan in TWOK.