Hi Don
I think the quote from Nick refers to a guiding principle rather than an absolute set of rules. His experiment was for a limited area of home/allotment but he was interested both philosophically and practically on the feasability of the principle on a much lager scale, even to farming systems on a world scale, particularly in developing countries.
If you want ‘a really definitive answer’ and quibble about the use of terms such as ‘as far as possible’ then the idea of this guiding principle is possibly not for you.
Charles also uses his method as a guiding principle rather than as a set of absolute rules. On the front page of the website is a photo of Charles holding a splendid bunch of parsnips and his expression is more one of delight for his crop rather than concerns about how he might have disturbed the soil a little in getting them out!
Thanks for the comments on comfrey which I have been cropping for some time. In case others are reading this it is important to note that not all Russian Comfrey is sterile. The Bocking 14 variety is recommended by most garden writers.