The origin of Fabrizio Salani's "AG" monagram

[Jorge_Stolfi]

In short, the wax seal is very close to Design 5, but maintains more properties of Renoir (Design 1).

Indeed. 

This leads me to hypothesize that the design of the stamp used to make the wax seal was post-Renoir, and closely related to Design 5. But everything remains possible - maybe both Renoir and Design 5 are based on an older seal.

I suppose that the seal maker had their own designer, who extracted Design 5 from the book and edited by adding the much-needed serifs.

All the best, --stolfi