I would say that its up to the whims of whomever is attempting to restore a lamp…after all lamp shades can be used is so many ways it isn’t even funny & many simply use replacement shades with a base. I’ll bet ½ of all the slag glass shades you see in malls are marriages, you’ve found a good proper period base & you ran across a good period slag shade that fits so why not marry the two? Case in point here is a huge Pairpoint fine arts banquet lamp that sits in my living room. The base weighs 27 lbs with the glass silver & marble & the spread of the silver candlestick trident is 16”. I had it a decade looking for a glass shade that would fit & if I wanted to “restore” it with an original Pairpoint shade (1) I would have to find one…good luck with that & (2) if I did find one I would have been out $1,500 to $1,800 for the shade. Two years ago I walked in a small mall & found this high domed 19” glass shade for $80 & finally after a decade I had my lamp complete. It just all depends.
While I am on the subject & I am speaking of the U.S. only here…95% of all lamp manufacturers did not manufacture the glass components of their lamps…they subcontracted with existing glass manufacturers, Cambridge, Tiffin, Heisey, Duncan, etc. whereby they sent the molds to the glass manufacturer for the pours & then had the molds & glass parts shipped back to them for assembly so identifying whom did what for whom is pretty much impossible since subcontracted job records were not kept by glass manufacturers. There were exceptions of course, Pairpoint, Aladdin, Jefferson, etc. had total manufacturing operations, metal & glass, but that’s the exception. Hopefully this gives you a better idea of what you are up against when it comes to lamps in many cases.