"I am afraid that I do not really believe that County Clare was cut off from the rest of the world"
As far as farmer singers like Tom were concerned, it might well have been
You appear to be dismissing Tom's approach to his singing to make a tenuous point
I suggest you listen to Tom at length on The County Clare website and see how likely it is that he would sing American versions of songs.
Plenty of them available
Tom died in 1990 aged 83 - with one exception all his songs were learned as a young man - he filled out a fragment of 'Constant Farmer's Son' from a neighbour's version some time in the 1940s
I can't think of one of the singers we recorded who would have learned songs from 'folk magazines' or the radio
Jim Carroll