dadiOH wrote, on Sun, 12 Oct 2014 05:42:54 -0400:

What newsreader are you using?
Pan.

If a thread is one in which I am interested, I "watch" or flag it.
Pan can do that (although I don't use the feature).

Sorting set to "Sent" in descending order then "Watch" gets me threads
sorted from newest to oldest with watched treads grouped on top.
I'm pretty sure Pan can do that also.

I just sort by last in on top, but it's threaded, so, all responses go
into the threads.

I have my reader set to keep headers for 30 days.

Me too.

If someone replies to a thread for which I no longer have
headers, the reply is shown unthreaded,
sorted by the date it was sent.

Maybe that's why the very top of mine has single articles from
threads a million years ago. Most I ignore as they're really old.

If I'm not interested in a thread, I don't care where it is
or what does or doesn't show up

Me too.