Sometimes users post messages 6 threads that has already been posted by someone else. When this occur I like to join these threads. In some cases the thread is weeks old and I couldn't figure out how to join this old thread with the newly posted one because selecting the first message of the posts doesn't seem to add it to the "to join list" when there are to different posts on different threads.
Maybe I'm missing something and this is a dumb question. But as far as I can see joining threads is not possible.
Merging threads in forum list example (http://xenforo.com/community/forums/suggestions-tweaks-small-features.18/) that is easy when they are near to each other for selection. But merging an old thread with a new one, expecially when this old thread was posted months ago and you have to search to find it... Going through a lot of pages is a painfull thing to do. Selecting the first messages of the threads seems not to work. Sorry If I wasn't clear enough before.