I have a Ferlib, not a side lock,a 20 bore "Superposed" and have trouble finding value as well,keep an eye on the GI list and you can also write them, the owner did answer me and told me when it was built and where the engraver(Piardi) is now and what it cost then;
here is the link,he does not write perfect english but was very helpful;
http://www.ferlib.com/htm/iniziale.htm

here is mine;
http://www.hunt101.com/data/547/DSC013151.JPG
http://www.hunt101.com/data/500/DSC01324.JPG
http://www.hunt101.com/data/547/medium/21780Ferlib_L.JPG

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