When I was looking on one of the FW sites I believe it was a Singer site. It stated that the scroll faceplate and the plane faceplate (the exact name escapes me at this moment) could very well been manufactured the same day and next to each other. Seems that Singer used bulk bins to stock the faceplates and other parts and when the supply was low in the bin they would add more plates. Leaving the previous ones at the bottom. When the bin was again low then the face plates could possibly be mixed again. Rotation wasn't important as they were making 50,000 or so a year.
One just looked a little prettier than the other, no big deal if I wanted a scroll one I could just go online and buy a different one. Noone would be able to tell if it had come with it or not. Mine was given to my Mom by my Dad new and then from her to me.
My FW is priceless no matter which faceplate it has.
If I were looking for a FW I don't think that a faceplate would deter me from buying at any great price one way or another.
Not saying that the scroll faceplate is not representitive of a specific year, just saying that some of them could possibly be any year.