I believe that 'learning from a source singer' can be a misleading term if not thought through
We have to face the fact that many of our older singers were way past their prime when they were recorded, even the best of them, and many of them were remembering songs they hadn't sung for decades - physical problems were often a feature of their singing (though some of the best singing I heard from Harry Cox was done in the later sessions at a full 'Windmill' pub - circumstances can make a difference)
I hated hearing younger singers trying to sound like Harry or Sam Larner - who wants to sound older than they actually are - that'll come too soon anyway?

That said, it doesn't mean you can't take aspects of singing from the singers that wouldn't come natural to townies like us
The older singers seemed to have a feel for interpretation that I find lacking in far too many younger, more technically 'skillful' singers
Health permitting, the old crowd tended to phrase their songs perfectly - punctuation in the right place, no artificial gaps in the line - musical storytelling
We have a recording of Tom Lenihan 'telling a song' - talking and singing it to explain its meaning - you can follow the story perfectly

They also tended to pitch their voices around their 'natural' physical voice (I wish some of our 'breathy' women or over-nasal male singers would learn to do that)
The Critics Group spent a long time working on making a song our own, interpreting it so you were able to relate to it personally
Singers like Walter Pardon, Tom Lenihan and Mikeen McCarthy had done it all their lives without having had to work at it apparently
They saw and relived their songs when they were at their best - they sang for themselves

Imitation of singers can be useful in exploring and understanding your own voice, but as far as I'm concerned, that's as far as it goes

These are our observations and my opinions - I'm sure there are plenty of exceptions
Jim