Traditionally the upload system has taken it on faith that the person reporting has won the game, and has done zero validation on that front. The reason for this is because its not possible to detect with 100% certainty who actually won the game just from the replay.
To help reduce the number of cases of abuse with people falsely uploading their losses as though they were wins, there's a new system in place that validates actual victory, using a number of guesses and heuristics. It should be accurate in around 99.9% of cases; in other words, I estimate around 1 in 1000 games that you legitimately won, the system will reject due to believing you to have lost. In this case a support thread will need to be made to have the game added manually. On the other hand, it is now much more difficult to abuse the system by reporting losses, as the system will reject games that you haven't won
