Zed inconsistency's?

Played Zed in an ARAM noticed that there were weird occurrences when it came to the attack damage calculation bonus from his ult's passive.

Here's how many stacks I had prior to ulting - https://gyazo.com/27370f06ab6d857ac6cde13c65129c16 How many stacks my mark had - https://gyazo.com/63c6023e826c329145256b679529a792 And how many I got after the kill - https://gyazo.com/b746a2e4881c4fe7e7c4b7bed4072647

At level 16, the passive reads "5 (+ 15% of target's AD)" 5(246x0.15) = 5(36.9) = 184.5. I know Zed having that much attack damage late get is wild, but the math doesn't add up, and speaking of math that doesn't add up. I added up all the damage I should of had at the end of the game and ended up with more attack damage then I should of. https://gyazo.com/0bab220d07643e5098cd0351324f2e26 107 (level 17 Zed base attack) + 42 (Zed's Ult Passive) + 180 (Items) + 10 (Natural Talen mastery) = 339. I have an extra 16 AD.