I think with the birds above though- they used 2 colors of actual orps to make splits, which just happen to be unaccepted colors, to eventually get whites. We are doing the same thing with buffs in the ameraucanas. They are 100% ameraucana genetically, btu the in-between generation just look like mutts.
I am not familiar iwth the split white project though, so I can only assume they used all orpingtons.