I am wondering about this two, because I have just received the check-in notifications for two flights that I will take in 30 days time. So, I am going to do this live and report back here with the results!

ETA - And here are the results! I have checked in exactly one month before the following flights:

MAN-BFS Seat 19B
BFS-EDI Seat 19F

So that's one middle seat, then one window seat. Not too bad, that's a 50% success rate at having a decent seat and anyway, these flights have a timetabled block time of just 50 minutes.