I'm flying MSY - IAD - YYZ on August 20th. My original reservation shows MSY - IAD is UA740 and IAD - YYZ is UA2420. After calling in to upfare I now show that MSY - IAD is also listed as UA2420.
Original reservation
after change
I've checked on Google flights and it shows the MSY-IAH 16:01 flight as UA2420 on August 20th, while showing it as UA740 on every other day of the week. A new search on United.com also shows the different flight number on the 20th.