@afullo. Indeed, it can not verify if the finish has been crossed. That's why verification has to take place. Check my replay below (i apologize for polluting the replays) I just stopped driving half way and saved. This is off course useless as a cheating mechanism because it is very easy to see.
Hmm, but in the case the platform would not have any mean to recognize it as invalid, since it does not run the lap to verify that the finish line has not been crossed...
This is a cheated replay to prove a point.. (added 45 seconds penalty time to compensate)
Pressing ESC at the end of the race cuts your replay and makes it invalid. The time after finishing is always the same and has no inputs, this is automatically corrected. If you upload a replay that is cut short, too much is corrected and that results in a lesser and incorrect time on the scoreboard.
As already said, don't press Esc before ending the second after crossing the finish line, because pressing it would not result in having 20 final frames without inputs, which is required to deem the lap as complete.