1.1.1+1.20.4 (and I believe I had the issue when on 1.1.3 as well)

It seems that while attachments are copied in ItemEmiStack#copy thanks to calling the ItemStack#copy method, the way the data of the stack is persisted and recreated in EmiStackSerializer leaves out the separate attachment based NBT that NeoForge adds. For ItemStack#save and ItemStack#of, neo makes the attachments get saved to the nbt, but it doesn't cause it to get serialized to nbt every single call to getTag. I noticed this issue while investigating why the filled variants of Mekanism's items were not displaying in EMI even after defining comparisons for the stacks. I don't know quite how urgent this issue is, given while in 1.20.4 it doesn't work, I presume in 1.20.5 with the move away from raw NBT and to Components this will just be fixed natively.

Hm, after looking into more how much would be required to support this, I might put it on the backburner. 1.20.4 is a pretty dead version which I imagine will be replaced by 1.20.5 pretty quickly. I'll keep tracking on the issue if I take a proper stab at this.

I support 1.19.2 to modern, and I imagine this is an issue on forge as well, so it will have to be fixed. I'm very surprised it hasn't been noticed until now, but I suppose that's just because serialization is only really used for favoriting.

Attachments are a NeoForge 1.20.3 and 1.20.4 concept, that might go away in 1.20.5 in favor of mojang's components.

Nope, neo is moving away from this in 1.20.5