I suspect the vast majority of fiddlers, as today, just played tunes they had picked up from somewhere else (which they may have amended slightly, but that's another matter!) Greg, you may be interested in a fiddler's manuscript book I have from about 1805, probably North Yorkshire or thereabouts which I have scanned and put up as a webpage for people to look at. (I think you said somewhere else that you do not have full internet access so send me a PM if you would like me to email you a tune list). There is a tune list and a scan of each page (which may take a while to load as I wanted them to print out at a decent quality).
Click here
From the way the tunes are written (mistakes etc) it looks like he was learning them by ear and writing them down from memory. I don't think there are any original tunes in the book although there are one or two I still have to find elsewhere.
Lynn