There can be an assortment of dates on individual messages within a threadd, but the thread overall carries a last-modified timestamp--the timestamp of the most recent message it contains. The TOC display algorithm works on the last-modified thread timestamp to divide threads into two groups: Those within the window defining recent activity, and those earler than the window. The algorithm doesn't sort threads within the two groups; they're displayed in natural posting order (the timestamp of the root post) within each group.

The description is the consolation prize because I can't precisely answer the question. Like a lot of simple algorithms (e.g., biological evolution), this one sometimes produces unanticipated or synergistic results.

I recognize that there's another part of your question, dealing with EP. Given the subject matter of the thread on which EP originally manifested, and the way he keeps referring to Nick's health problems in a totally unacceptable way, I chose to quietly disappear the most obnoxious of EP's posts. The alternative was to make a big fuss, which would be a disservice to Nick, and would let EP succeed in disrupting the place. I'm dealing with EP in private email.

Yeah, I know, doing a Gitmo on posts violates my standards of transparency and accountabily. Guilty as charged. Sometimes ya gotta follow your conscience even if it means breaking the rules, and in this case, to me, shielding Nick from EP is a higher calling. So sue me.