Geurt, have you ever found out when the various styling changes took place? Looking at the York's, there seem to be a couple of subtle alterations with the older body style, (York being in a rectangular rather than oval recess, and patent info instead of the model No. on the other side), and then there was the change to the newer, less rounded shape. Any ideas as to when the changes took place, and in which order they appeared with the older, rounded style? There doesn't seem to be much info on the York's in that regard.
Also, with the older style, any idea what the A suffix on the model number infers? Looking at photo's of say an 80 vs 80A, I've not been able to note any physical differences. I may well be overlooking something obvious though.