If it's any easier to just delete everything, with some printers there's an option to "print table of links" when printing from a web page.
With my setup, when I click Print, I get a window that lets me chose which printer, with a "General" tab and an "Options" tab. On the "Options" tab, putting a check mark in the box produces a print of the page (or the selection, if that's picked) followed by a table that gives the "display text" in the left column with the URL in the right, for each link in the printed area.
This would provide a backup printout listing all the threads you've traced, with the URL for each, that you could refer back to if you accidentally detrace one you want later - at least until the cat tips your coffee over on the printout.
(I'd probably scan the printout and OCR it to text, and let Word convert the URLs to links so I could "click" back to them, but OCR isn't 100% accurate - so I'd save the scans too.)
If Joe can figure out how to run a multi-link detrace, that would also be one way to extract all the thread numbers for the ones you want to remove from your list.