...Now your point about ordering parts - there is evidence Apple did that year(s) ahead of time - how do we know - here it is MC's favorite analyst Kuo talking about this iPhone X in March of 2016.
https://www.macrumors.com/2016/03/26/kuo-iphone-2017-oled-curved-glass/
Yes, he was talking about OLED screens. Samsung had to have plenty of notice in order to build and convert factories.
OTOH, orders for FaceId parts didn't begin to show up in the news until (late) summertime this year. E.g.
https://www.macrumors.com/2017/08/09/apple-massive-orders-3d-sensing/