Doh! Typos in the above (Thackery is the wrong spelling used by Robbie, but Thackrey is wrong anyway - Thackray is definitely right!)

Last para should say "...JT was not the original source..."

What I was trying to say was, if someone can point to a book dated before the 1960s (or better, before JT's birth date whenever that was - 1940ish?) that mentions the 'sheep' counting system, that would prove it wasn't just JT's own invention.

My belief is that he didn't invent it, just the story about Molly Metcalfe (and of course the song about her). But I admit I can't prove it as I don't have any evidence!