A search box above the history searches the full text of every transcript kept on the machine, not just titles and channels, and narrows as you type.
Each result shows the phrase it matched, with the words you searched for picked out, so you can tell the right video from a list of near-misses before opening anything.
Re-transcribing a video used to shove it back to the top of the history as though it were new; it now keeps the place it has always had.
YouTube Caption Bot