Didnt know if the title makes everything clear. But you are able to complete all Darkmoon Faire quests (artefacts and profession quests) from the month before:
example to understand:
1. Darkmoon Faire starts at 23.59.
2. Dailies reset at 03.00
So there is a time period of 3 hours. During this 3 hours you can complete the darkmoon fair quest from AUGUST although its the darkmoon fair for SEPTEMBER. After 03.00 you still got all quests available for September.
You can only complete the quests if you havent done them before, during august.
So this is basically a method, if you forgot to turn in some quests or if you didnt made them at all.
Hope this is no repost, i just realized this yesterday while everyone was yelling "Where are the quests"