Fortunately, more detailed information has appeared. I recommend Flying Saucer Aircraft by aviation writer Bill Rose. In it, we learn about Alfred Loedding who worked at T-3 Engineering at Wright Field. A fluent German speaker, he interviewed German aviation experts after the war. He was also asked to head the first American effort to investigate UFOs, which he called Project Saucer, but later the name was changed to Project Sign. A photo of him sitting next to a model of his disc plane appears. Also mentioned is the work of Frenchman Rene Couzinet who designed a disc aircraft. American intelligence was following his work. Details about Project Silver Bug are given, including the fact that it was given the same US Air Force project designation as the failed Avrocar. Photos of the engine test stand are shown.
I also recommend Die Realitaet der Flugscheiben by J. Andreas Epp. This man was developing conventionally powered disc aircraft in Germany during the war. There is an Air Force intelligence file on him.
The evidence is there but it takes a little work to locate it. It appears the Americans may have built a handful of conventionally powered discs for reconnaissance purposes. However, more advanced electric field propulsion discs were apparently completed and evacuated from Germany either just before or just after the end of the war.