I don't understand if iris should fix this bug

So, I'm creating this pack, in which various items take on different appearances when renamed. In this case, the pumpkin, if named "Poncho," becomes a poncho, "Cowboy Hat," a cowboy hat.
I noticed that only the first model called in the json is properly loaded. Also i noticed that items like the bow doesnt present this kind of problem.

this only happens in vanilla; with iris, everything works fine. why? the problem is that it doesn't load the hat model, only the poncho. Am I missing something?

In the json file inside the "items" folder, I created the json file to modify the pumpkin, using string mode. I noticed that Minecraft understands that it needs to change the model (in vanilla), but it doesn't (the buggy item in the image is renamed "Cowboy Hat") and looks like the game can't assign the corrisponding model to the item).

Can anyone help me? It seems strange to me that the game can't load more than one model for an item in vanilla, or rather, that it understands what it's supposed to do but can't find the correct model.
need-an-hand-with-custom-renamed-item-model-v0-h80n3rukh97g1.webp
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