One place on a frame that shows a builder's individual style is how the dropouts are attached to the blades and stays. A picture of that area would be helpful. Also Campy dropout edges are typically smoothed by the builder in some fashion. They could be squared or rounded depending on how the builder wanted them to look. It will probably be a particular combination of ordinary factors (for example the distinctive fork crown treatment and bottom bracket shell hole drilling) that can lead to builder identification.

Potential sources of knowledge could be painters that might recognize an individual's work.