I was trying to make a new texture for emerald with "Damage" value 1 (using new resourcepack model format), but I discovered, that items which are not intended for using that NBT tag, do not show their texture when this tag is not equal 0.

JSON file is from my resourcepack,
first and second screenshot shows normal emerald,
third and fourth screenshot presents emerald with damage 1
fifth shows item without using any resourcepack but having that value