>Do you think these issues could be overexamined sometimes?<

On the contrary, Brian has drawn attention to an issue which has very rarely been explored; which is not whether variations in folk songs occur, but how and why individual singers have introduced variations.

Dave Ruch's example of a singer "filling out" a fragment learned from a relative by reference to a printed source may be a more common practice than collectors have acknowledged.
Didn't Carpenter encourage Bell Duncan to come up with fuller versions of ballads by showing her examples in Child?
I think I've seen in Henry Burstow's 'Reminiscences' that he looked out for 'better' or more complete versions of songs he already knew by listening to other singers or buying broadsides.
Mike Yates recollected his surprise at spotting some songbooks on the floor when he visited Fred Jordan.

In general though we have very few examples of songs recorded in the same family or community at different times to allow any sort of diachronic study of how songs and tunes have actually been altered. The Copper family do show some quite subtle variations but in their case the existence of a family songbook probably stabilised the older versions so that their particular tradition was a very conservative one.

My own overwhelming impression on listening to older recordings is how much accents and speech rhythms have changed so that when, for example, Roger Hinchliffe sings the same songs as his father sang he is still singing from deep within a long tradition but in a different voice which brings that tradition into our own time.