I've long believed that they play this "change the flight # game every 2 months" crap as a way to reset their otherwise horrible on time stats for each flight.
There are many flights that I have taken in the past under multiple flight numbers but were still the same route + / - 5 mins to schedule, but now continually get new numbers every few months. Often, the on time performance data is unavailable, likely because it is too new of a flight.