Foglio lamp by Tobia Scarpa  

Hello,
I bought 4 Foglio wall lamps from Ebay (italy). The seller said taht the lamps are original from the 60s-70s. They really look old, but three of them have porcelain lampholders (photo 1) and the other one has nylon injection molded lampholders (photot 2).
I have never seen before those porcelain lampholders (with the number 1113 stamped on the bottom) on a Foglio lamp, but searching on internet I have found a Foglio lamp sold on Bottemberg auction house with those porcelain lampholders...
Do someone know what could that means? The lamps look real to me, so I don't know if that could simply be that the owners changed the original lampholders for any reason... or if that's a fake lamp.... or maybe an older/newer edition...
Thanks!
http://www.flickr.com/photos/101655387@N07/12882083235/in/photostream/