sleepyjon:
"Since playing for the Morris... I've been struggling to develop a technique of "using the left hand as a bow" - and lecturing about it to anyone who I thought would listen! - thought I'd invented it myself!"

Since You are talking accordion here it is selfevident that your "bowing" will be done by the left hand.I started with accordion too before having a concertina so I preferably use my left arm for bellows work also. Otherwise those concertina tutors who speak of "bowing" at all of course assume that it will be performed by the right arm - just as with a violin.Since "bowing" may be a very delicate task it seems efficient to prefer doing it according to individual handiness - either being left or right.

Concerning the historic background I mentioned Alsepti for (English) concertina. In the 'accordion world' you may find for instance Favier (Paris 1839) saying "The bellows is for the accordion what the bow is for the violin" and this expression is repeated among several of the Victorian concertina tutors. Back to accordion the most dominating author/tutor advocating ( very theoretically) for complex articulation with the accordion was Hugo Herrman who wrote about it in 1950s and he has been the prime "guru" in the field when accordion tuition became an academic discipline.

The concertina has never got the same academic basis as tuition for piano and symphonic instruments and this may be a reason that concertina players have few references to good performance practise.
In turn a reason that experiments and advise like these coming from Dick ( and your own experience) pop up individually and sometimes in the belief having "invented the wheel".