Ah I see, definitely missed that mention then when going through the Main Scenario Quests, although even assuming the most recent ones are proper it does make me wonder why Iconoclasm has them flipped given it was also created after such presumably (in regards to development) and is present in the First where such a relation was made.
Checking with a friend on the Japanese versions of the debuffs it seems Twelfth Circle doesn't explicitly use light/dark, but Iconoclasm does seem to being "偏属性 : 光" (Equivalent to Astral Effect) and "偏属性 : 闇" (Equivalent to Umbral Effect) seeming to still relate Astral-Light and Umbral-Dark even when being past such in story (not sure if the Eden raids mentioned something to explain this.)
Twelfth Circle in comparison apparently uses "極性偏向 : 霊" (Equivalent to Umbral Tilt) and "極性偏向 : 星" (Equivalent to Astral Tilt) which from what I understand the last word is effectively "Spirit" for the Light, Umbral debuff and "Star" for the Dark, Astral debuffs

Regardless of which (or even both if something allows for such) are proper, it seems odd the naming convention was retained in English but not Japanese (unless I'm misunderstanding the Japanese debuff name which is very possible) while flipping it from a previous iteration without seeming reason for such flip, since both Iconoclasm and The Twelfth Circle exist at a point after that Main Scenario quest in a player's experience, unless there is something past such a point that explains it (which it's very possible I could've missed such)