Article by Tom!.
I was asked to start a thread on this topic.
All informations and answers I give here are AFAIK after 7 years of research in secondary sources and discussions with several japanese and non-japanese experts, namely Akira Takizawa and Yasufumi Kunimoto.
There are still many things that I don't know and/or have to assume and/or I got wrong.
Corrections and questions are welcome.