It’s gotta be a big YMMV thing. I wonder if US airlines might do that domestically only but not for international.
Air Canada will renumber a daily flight if the delay goes past midnight (to avoid having two departures with the same number on the same day). I doubt it’s just a courtesy, but an incompatibility with their (or enough airports’ systems).
Air Canada will renumber a daily flight if the delay goes past midnight (to avoid having two departures with the same number on the same day). I doubt it’s just a courtesy, but an incompatibility with their (or enough airports’ systems).