There ya go.
My point to this is irrespective of what the RMK catalog says, the only collectible material is the Westinghouse material aka "Old Yeller". RMK has tried to replace that for decades with an "ivorite", but really has in catalog name reference only.
Like Cap says, the properties of the Westinghouse material are different than its replacement(s). The yellowing of the material is what sets it apart.
I get from the shop perspective, it is a white handle material like the rest, but it isn't, and hasn't been for decades. Again, my .02.