A last contribution from the Peadar who started the topic:
I was about to respond to Chris Ryalls suggestion that I answer as to whether the discussion had answered my question when Theo drew the debate to a close, so I am asking him to edit this message into the last post on the topic.
There was of course the inevitable digging in to established positions but I took something away from the points made by almost eveyone who engaged with the question.
I concluded yes you can look at it in that way, but regardless of how I see it myself, the approach makes most sense if you are coming from a musical tradition in which there is a predominant key to which your main row is adapted. Notwithstanding the Peter Kennedy's views on D&G as the most useful keys for folk music I personally think (probably wrongly) of C as the home key of traditional English music.
The B/C had seemed to me a rather strange choice for Irish and Gaidhlig traditional music, where instrumental keys have long been influenced by the easier settings for fiddle music (G, D, A) and the pipes (D). I found Richard Fleming's explanation that he sees the semitone keyboard as a single entity rather than two rows was genuinely enlightening, and though I doubt my psyche will ever comprehend it in that way it explained how the B/C works with Irish Traditional music centred round the key of D.
Others demonstrated quite different ways of understanding the keyboard...and I would like to say a personal thank you to everyone who contributed to the discussion.
