How often do airlines re-arrange flight numbers

Aviation Airlines
1

and I just wondered why ?

the flight I took to Dallas from Seattle is now the Denver Chicago run. Just started a week or so ago

12-Jun-2010 MD82/Q Denver Intl (KDEN) Chicago O’Hare Intl (KORD) 12:18PM MDT 03:20PM CDT 2:02
11-Jun-2010 MD82/Q Denver Intl (KDEN) Chicago O’Hare Intl (KORD) 09:47AM MDT 01:32PM CDT 2:45
10-Jun-2010 MD82/Q Denver Intl (KDEN) Chicago O’Hare Intl (KORD) 09:45AM MDT 12:35PM CDT 1:50
09-Jun-2010 MD83/Q Seattle-Tacoma Intl (KSEA) Dallas/Fort Worth Intl (KDFW) 09:51AM PDT 03:32PM CDT 3:41
08-Jun-2010 MD83/Q Seattle-Tacoma Intl (KSEA) Dallas/Fort Worth Intl (KDFW) 09:42AM PDT 02:58PM CDT 3:16

2

Not to be flip but whenever the airline wants to change the flight routing for a given flight number.

Some flight numbers hardly ever, if ever, change such as UAL1 or AAL2. while others change quick frequently such as many of the Southwest flights.

3

I’d say we change flight numbers every 1 to 2 months. Heck, we don’t even know the final schedule until less than a month before it changes.