It's even harder that FCfree makes out.

I wasted some time a few summers ago making spreadsheets for various WN schedules; it is easy to track the change in flight number when a flight number terminates at a small station, but when the flight number terminates at MDW or BWI (or LAS, etc.), there could easily be 5 possible new flight numbers that the original plane could be continuing on. So I wasted lots more time looking at WN's flight status indicator, trying to match up planes by the gates of incoming vs. outgoing flights. That worked great - except that when I looked at the same flight numbers on different days (in the same airport during the same WN schedule), they would connect differently!

I'll add a picture of my work if I can figure out how to post the image.