When I read spontaneous folk composition I thought of my unfortunate knack of forgetting words and ad libbing a bit.

I assume this is how songs tend to alter over the years. I have been singing a Harvey Andrews song for years and even when getting it right, I recently noticed Harvey has the odd different word. I think I I sang it as it was written back in the '80s but repeating the same ad lib line means it slowly becomes your norm.

I suppose that's definition 637 of what makes it a folk song...