TWA was a classic at keeping the same flight numbers. I can remember when I was a non-rev traveling on my father's pass. They had the classic "triple nickle" from STL to MCI and it was the last flight of the day. That flight was placed just for the Kansas City folks who commuted out of STL. The other one I can remember was Flight 1 to HNL and Flight 2 back to STL. Not sure AA will/has kept these flights.