The 12m challenge thread has not been closed because nobody has posted to it since the limit was changed last Nov 2017. You can see the last post was made “Sep 11 2014 11:23am” by Gerald. If someone posts to it now, their post will be accepted and then the system will close the thread. This is as the limit is set to 100 replies, i.e. the original post, 100 replies and 1 close message from system.
“North America <> Europe SOTA S2S Party - 19th November 2016 1400 - 1700 UTC” is open at post 421, last post Jul 16, '17 6:17 PM
“What is the highest QSO total of single activation” is open at post 330, last post Mar 26, '12 3:21 AM
Whereas “Datamode - FT8” was closed at post 220 on Nov 26 2017 after the limit was changed and, in this case, I posted to it.
There are currently 54 threads active with a reply count of 100 or greater. They’ll remain open indefinitely unless someone goes and posts in them. Then after that user post, the system will close the thread.
But hey, that’s nothing but facts and who in their right mind would argue a case using facts.