Question: About Old Paris Metro Maps

David Kim asks, “I was wondering how valuable old Paris subway maps are, in general (if such a question can even be answered)? I am talking about the 1937 map of the Metro you had on your site a while back?” (He means this one.) He also asks, “Is there a web site on antique Paris Metro maps?” I didn’t know of any; a cursory Google search in both English and French came up with nothing. Is there an RATP specialist in the house?