I'm looking for information regarding Philadelphia Mint souvenir visit medals, issued from the 1920's through the 1940's. These were small bronze pieces, 33.2 mm to 33.8 mm, that featured the portrait of the President (Harding through Truman) used in the Mint's Presidential series on the obverse, and either a defiant eagle or third Philadelphia mint façade on the reverse.

Some of the medals are dated, some are not. I understand that the late Assay Medal collector and expert Ernie Keusch identified 17 different medals in the series. Does anyone know if Keusch or anyone else ever published anything on the series and, if so, where and when? I've attached pics of typical medals from the series.

I've written before about the lack of comprehensive reference materials regarding the medallic output of the United States post Julian. It's pretty amazing to have this sort of gap, but also pretty cool trying to tease out the history without it.