Yesterday in a local tournament at the end of my first round I filled out the score sheet with my opponent reporting my victory to the judges.

After 10-15 minutes, when I was already setting my things for round 2 the judges inform me that there was an error in my report because in the last turn I forgot to activate the effect of Stunned Pilot in my last ships(large one), giving the victory to my opponent for a correction in the points count(the last damage made half points).

Is it legal to do that? The Stunned Pilot was public information and the judges ignored the responsibility of my opponent, it was a mistake of both. The game had already been concluded and both players had already agreed to the result.

I imagine its down to TO discretion and really, probably the right thing to do.

Maybe it's "public information" but it's one of those things you control, is NOT optional, and which ignoring provides a benefit to you. If that point of missed damage is also what put a large ship under the half-hp threshold (not that I agree with that concept to start with) it is very significant although your opponent may not have thought about it as much. Had the game continued would you still be arguing against the application of that damage?

What does have me scratching my head here is how did this error finally get "caught" so far into the next round? Once caught I believe it should have been corrected but what led to its discovery is what has me wondering.