As long as nobody makes a newer post in the thread, the poster of the last post in a thread can edit as many time as he/she wants without any "Last edited" message appearing.
And this makes perfect sense because if say 2 members are engaged in a heated argument (which is quite often happening in this forum), one of them makes a fatal logical mistake in his/her statements, the other can attack that point and make the former look really stupid. If the 1st member then decides to come back and edit the original post to erase/correct those faulty statements, there is still proof that the post has been edited so the 2nd member can still claim the first poster as wrong. (In practice if you really want your enemy to look stupid you'd probably also want to explicitly quote his mistakes so that he can't do anything to hide them.
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So now that I've replied this thread, you can no longer edit your post above without people knowing! Not that there is anything wrong about your post though.