I can't speak for the other champs, but I believe I can explain Darius.
Let's start with the "higher" of the two defense numbers Darius has. At level 18 he has base 97 armor. It's safe to assume that, like most Darius players, you can add 10 to that from armor seals, so 107.
makes 207,
makes 257,
makes 317 and
finishes it off at the 347 you see there.
So how did it drop?
Well, the armor changes actually have to do with your team, not Darius himself.
Two of your guys have Black Cleaver. This, as I'm sure you're aware, can cut up to 30% armor from a champion. 347 * .7 (Basic equation that removes 30%) = 242.9, which the game rounds up to your 243.
As for the spontaneous 200 attack damage: Judging by the killfeed, I'm willing to say it's a safe bet that he just killed Braum with his ult? When Darius' passive procs, it gives him bonus attack based on his level which at 18 gives, you guessed it, 200 attack. This is why it's so dangerous to be in prolonged fights with Darius or engage him after he just ulted somebody for the kill.
Now we know, and knowing is half the battle! Or something like that.
Edit: Just looked at the other screenshots. You only provided one screen of Kat so I'm not sure what you want me to look at, and Maokai bought a ton more armor between those two screens so unless you mean another stat, I dunno what you want me to look at there, either.
P.S. spreading the damage types is your friend. I'm surprised Darius didn't have a better K/D/A going against an all AD team and being able to skip out on MR.