The current W231, HP-38 and Zip are all being made at the same plant.I have shot lots of W231, none of Zip. Someone else will have to test this, but it is entirely possible that W231 is the same as Zip. As W231 is the same as HP38.
Same powder, different bottles. Won't be the first time. Won't be the last time.
There are a lot of powders out there which are the same but are under different labels. Years ago we didn't know HS-6=W540 and HS-7=W571 but it's true just like H414=W760... (and W231=HP-38 that we already mentioned)