When I said different, I was meaning different from my experience. I believe this is the first White Rotary I've seen, at least to study.
Are the machines you have similar, with end-caps rather than faceplates? Have you ever disassembled the needle and presser bar mechanism? It appears to me, with the removal of two screws, the end-cap containing the needle and presser bars will separate from the arm. Am I seeing this wrong?
I'm sorry I can't direct you to a manufacturing date resource. Perhaps someone here having more experience with Whites can.
Thank you all for your responses.