Internet research between library visits has yielded information on teaching and choral singing networks.
Today keywords for this search in the EUL were andragogy or adult learning and choral singing.
There is a whole shelf dedicated to this. I need to decide which aspect of the field I want to examine in order to spend my time wisely. I will read further the text by Scott on Madrigal singing and choose the aspects to look at in the context of current practice.