The right/left horns, and all four legs of cow variants cannot be independently retextured

(Because cows were added in Minecraft Alpha 1.0.8 before texture packs existed, this first appeared in Minecraft 1.2.2 Alpha for cows, Minecraft Beta 1.9 Prerelease 1 for red mooshrooms, and Minecraft 19w08a for brown mooshrooms)
The right/left horns, and all four legs of the cow, red mooshroom cow, and brown mooshroom cow cannot be independently retextured from one another, making them always look the same, limiting the player's resource pack creativity.

Steps to Reproduce:

1. Download and apply the following resource pack:
   CowVariants.zip
2. Spawn one of the following:
   1. Cow
   2. Red mooshroom
   3. Brown mooshroom

Observed Behavior:

Both the horns, and all four the legs of the mooshroom will look entirely red, despite the player seemingly only modifying one horn and one leg in the UV map.

Expected Result:

Only one of the mooshroom's horns and legs would be altered, since that is what the player intended to change. The current behavior is unexpected and not resource pack friendly.

Screenshots/Videos:

Notes

As of 25w05a, this also affects the new cow textures/models