You've previously posted in the Serious Discussion section, and any posts in that section, and it's child boards don't contribute towards post count. Other than that the thread is almost certainly being trashed. Your post count isn't being miscalculated.
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Serious discussionBitcoin Forum > Other > Serious discussion >
Ivory TowerThese are the two boards, Welsh was explaining earlier.
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4 etc are some examples.

Ok, so posts on ANN threads, of which I am currently moderating and updating do not count. Ivory and Serious do not count. I am ok with that, in fact I am asking this out of curiosity because I do not care at all about my post count for practical purposes.
But, the "trash thread" thing is a bit more intriguing. How do I know for certain, apart for my own judgment, that a thread is considered trash.