I think some of em won't get released until Phase 2 of the event

i can't see any of the mentioned or imma too much boomer to notice

O4-at the banner when you choose quest

Note: the devs lied about them all being inside the game.

K2-main page rotating banner

is the T5 in the ultimate level quest title part of the code?

T3 -- On Frozen Chocolate Gacha info description.
This one is not even hidden it's literally in writing next to "Frozen Chocolate!" , so it's different from the rest of the ones listed here.
The picture was posted on the Weekly Gacha thread but don't think anyone noticed it.