I've noticed that immediately after the match "Victory"/"Defeat" notification, there is a brief period before the winner screen shows up where you can still get kills on some players. You can confirm the kills with the sound that you hear when you kill players.
Do these kills count towards your match total?
For example, if I get 30 kills as Reaper and the "Victory" notification pops up, and before the winner screen appears I complete my 31st kill against a Mercy, does the game record me as having made 30 or 31 kills during the match?
Best Answer
No, they do not. I have tested this myself, as I got killed at the very end of the match after the Victory animation came up, and I was kind of upset because I hadn't died all match (gotta keep that perfect KDA). Then I checked my stats, and I had no deaths for the match. So no, killing or dying after the victory/defeat animation starts does not count towards the stats for the match.
Note: As @Schism states, this is true for all stats. For instance, getting hooks as Roadhog after the match end does not increase your hook percentage or count.