can't splain, but I know Henry mostly refused to use any unique product from outside suppliers unless they let him "buy the rights", so maybe there was a FoMoCo glass division that made the flat glass [yes it does mean Ford Motor Company]
some glass logos , usually included a date code - I've never noticed any Chevy glass with the FoMoCo logo, but I'll ask a buddy who's very expert on old Chevs [nicknamed "Mr 39" actually
]
yes, tempered glass has to be first cut to size then tempered [heated and annealed] ... but oddly enough after tempering it's easier to scratch than before
