I am making a World 1 hack with level icon ID edited with RicBent's Goombatlas. So basically:
1-Cannon -> 1-A
1-A -> 1-B
I only changed the icons of the levels, and I didn't mess with the level IDs. So I am still using slot 1-Cannon to make 1-A.

I used  skawo's Custom Level Intros with Player Select, and I made the preview screen for my now known as 1-A level. I inserted the ENPG ID in the slot "World 1: Cannon" in the code's table, and I found it wouldn't show up when I entered my now known 1-A level.

Desperately, I moved the image ID in  skawo's code from "World 1: Cannon" to "World 1: A". I compiled it then I opened the game again, and it worked!

So, the game is not reading which level slot you built your level in, but instead looking at which level icon you are using!

Edit:
I think it also explains why Nintendo made a terrible Tower 2 logo only for one level in one world.
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