Koga changes aces between gens. He truly has no two aces at once.
Brandon's a gimmicky trainer.
Flint's ace is Magmortar. Infernape is only there because Gen IV initially lacked Fire-types to justify his poor lineup of Fire-types (which the anime decided to make Infernape his ace just to have some link with Ash's).
N's "ace" changes between versions, but he never has two.
Korrina's Hawlucha pretty much fades into obscurity once she introduces Mega Evolution, because no one really has trouble dealing with the bird at all.
Red is a strange one, but his ace shall always be Charizard to associate him with his color-theme naming.
Also, having two aces defeats the purpose of having an ace at all.
So basically what I'm getting at, these trainers have two or more ace Pokemon. Let's take a look at each one.
1. Actually Koga has both Golbat and Venomoth in Gen 1 and Crobat and Venomoth in Gen 2. Not only that but this has been very consistent in all his appearances in whatever timeline he appears in.
2. So basically he has three aces.
3. So basically Flint has two aces.
4. So basically N has two aces.
5. So basically Korrina has two aces.
6. I'm starting to see a trend here that your reasoning is, not to be rude, "lacking" in attempting to justify that there can only be one Ace. Also Red has never had Charizard as his ace in the main games. It has appeared on Red's team but never as his ace Pokemon.
7. Correct me if I'm wrong but Ace means the simply the best right? Not there is only one best right? But if we were to go by the second meaning, by your logic we should stop calling them Ace Pokemon since GameFreak has rendered that term useless and start calling them Signature Pokemon right?