Cassina has their own guide for distinguishing originals from copys + a page about authenticity.
http://cassina.com/en/lc-collection/authenticity/how-to-tell-original-fr...
http://cassina.com/en/lc-collection/authenticity/identity-card-and-ident...
I'm not much in to Le Corbusier, so I can't tell for sure if Cassina is the only company who has ever made genuine LC4's.
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