If my memory serves me correctly, the Magnacut mule could be rusted in some situations, then a year went by (a year surely full of effort figuring out what they could do with it), then it ended up in the Salt series.
The same guy designed both and they both likely had approximately the same target for corrosion resistance.
So Magnamax being in the Salt series doesn't seem completely out of the realm of possibilities quite yet. It's still early in the game.