Originally Posted by
zrh2yvr
I can see the problem here. If a flight is delayed until the next day, a new number will always be assigned because you can't have 2 flights departing on the same day with the same number.
Actually, you can have 2 flights with the same flight number / call sign departing the same day. Look at AC33 / AC34 for instance. Same flight number, departs on the same day, but the 2 segments are never in the air at the same time. Or what US carriers do with their flights with one flight number, with different segments operated by different equipment. What you cannot have is 2 flights with the same flight number / call sign in the air at the same time.
Air Canada likely renumbered the flight (by adding a character to change it to AC868x), but it wasn't reflected on the information screens and in the App. However, if you were to look at Flightaware or another flight tracking tool, it'd show up with the revised flight number.
Happens all the time, never had an issue with this. Sometimes, it's renumbered AC2xxx (so if AC34 is delayed leaving SYD, another plane would have operated AC2034 if they did not want to delay the YVR - YYZ segment), sometimes with just a character appended to the flight number.