There is an excellent Paramount history on the Waterford website and the lug changes are covered. In short, Schiwinn switched briefly to Prugnat lugs and bottom bracket shells on Paramounts because they required less hand finishing. Customer outcry required that they switch back to Nervex lugs but they kept using the Prugnat bottom brackets. I have one of each of the latter two and my older Prugnet version looks "newer" than my newer Nervex version owing to the relatively simpler Prugnet lugs.
Randy
Corral De Tierra, Ca.