Either I've missed something or damage calculation is incorrect [contains math]

EDIT: Everything seems normal, ignore my ramblings.

First off, I want to say this disclaimer before I get idiots who miss the point of this post: -I am not saying I should have survived this situation -I am not saying I deserved to win this game -I am not saying that even there is an error in damage calculation, it would have made a difference in this match (after all it could be benefitting me too) -I am posting this to see if there's anything I failed to take into account. I tried to be as pedantic as possible. -I am not complaining about the fact that Xayah did that much damage. She was a full build ADC.

Alright, now that I (hopefully) made my intentions clear:

So just now I was in a game with a very strong enemy Xayah. I positioned poorly thinking I could catch her and got melted. Out of curiosity, I went into the replay to see how much damage she was doing to me (because it was damn impressive). Unless I've missed something (which is entirely possible, and if anyone can point it out please go ahead), the damage being calculated by the game is wrong.

Here are three screenshots: https://i.imgur.com/6KnHQLC.jpg

https://i.imgur.com/2KAwrXR.jpg These two are of the same moment, one with me (Darius) selected and one with the Xayah selected, so you can see the stats of both. As you can see, at that moment she is critting me for 499 damage and I am about to be extremely dead. You can see she has 419 AD and I have 262 armor. You can also see that Xayah has two zeal items, an Infinity Edge, and an Essence Reaver, putting her at 100% crit.

https://i.imgur.com/EE2V9Wf.jpg This screenshot is her attacking a minion only moments later. For some reason, her AD is 428 now, but it shows that with that much AD, she does 1076 raw damage with each autoattack. This makes sense, as 428 * 2.5 = 1070, and champions do an extra 5 or 6 damage to minions (I forget which). The 1 damage difference is easily explained by rounding. This shows that the crit multiplication on autoattacks works as intended.

So lets establish a few numbers: Xayah has 419 AD when she attacks me. I have 262 armor. As a level 17 Darius, I have 102 base armor. This puts me at 160 bonus armor. Xayah has a Lord Dominik's Regards, giving her 35% bonus armor penetration. I was debuffed with Press The Attack, increasing my damage taken by 12% Xayah had Coup De Grace, increasing my damage taken by 10% since I'm clearly below 40% HP.

My effective armor vs her: 160 * (1 - 0.35) + 102 = 206

Damage taken from physical attacks at 206 armor 100 / (206 + 100) = 0.32679

Base Damage of Xayah crit with 419 AD 419 * 2.5 = 1047.5

Damage of Xayah crit with all damage increases 1047.5 * (1 + 0.1 + 0.12) = 1277.95

Damage taken after mitigation from armor 1277.95 * 0.32679 = 417.63

Since Boards does not offer a good format to show math, I also made this image: https://i.imgur.com/v5zMzO5.png

Based on my calculations, there is something accounting for a 19.4% increase in Xayah's damage output. I double checked everything, items, runes, etc, and could not find a culprit. It wasn't Ardent Censer from the Soraka, as that would show up as magic damage and would not be this much even if it was showing up as physical. Nobody on her team can give her autos more physical damage.

I'm not very familiar with Xayah, so I checked the wiki and it did show her W, Deadly Plumage, has an effect that "creates a storm of blades for 4 seconds that grant her attack speed and cause her basic attacks to strike an additional time for 20% damage." However, at the point in time where I took the screenshot, the Deadly Plumage buff is not on her, as it had timed out. Furthermore, if it was Deadly Plumage, it should be doing 503 damage, not 499. That's a much smaller error, but the buff should still be on the buff bar.

TL;DR Either I missed something (entirely possible), Xayah's W has a bug causing it to apply after it times out, or damage calculation is bugged somehow.