Once airlines began being nailed for having chronically delayed flights by USDOT, they became crafty at changing flight numbers, and I would guess times as well, to avoid being on the "most wanted list."

See Page 13 of this report, the March 2018 Air Travel Consumer Report: https://www.transportation.gov/sites...rch-atcr_1.pdf

No offenders. Can't have a chronically delayed flight for months at a time if you change flight numbers/times/etc.

Here is what happens when the flight information isn't scattered, see pages 13 and 14: https://www.transportation.gov/sites...ember-atcr.pdf