For me, TAS was the beginning of a new 5 year mission. TOS, I felt completed it's 5 year mission. Stardate in Where No Man has Gone Before begins with 1312.4; I would like to believe the first numeral was the year for the space missions. Stardates started accelerating because the production feared they won't reach the 5 year mission (season) goal, by season 3's All Our Yesterdays the stardate was 5943.7. The numbers don't lie and it's enough for me.
A second 5 year mission in TAS would be more likely since the Enterprise presented obvious upgrades which were later realized in TMP, plus I think there were some uniform alterations as well, and the stardates were consistent to what was established in TOS.