You cannot create a duplicate thread of one that is currently in use. If the thread has not seen any action in 30 days, it is not considered in use and you can start a new thread. Threads over 30 days old have no information in them. MMOs are constantly changing; so a 30 day old thread may be completely inaccurate to current gameplay.
But if what you want to talk about is 30 days or older, then you can start a new thread.