"just never heard of Jimmy Buffett (or Jerry Jeff Walker).   Never heard the song either."

Neither have I. Some people seem to find it hard to accept that just because something is reasonably well known in the States it doesn't mean it is known the world over. Someone said from a UK perspective Buffet was a one hit wonder - but to be a one hit wonder you have to first have a hit. He has had no hits here! Just checked the Guiness Book of Hit Singles and Albums and he's not listed. Not even in the bottom echelons of the charts. No presence at all. Plenty other songs haven't been hits but are well known but again like you, this is the first time I've even heard of the song. If it was getting played 'a lot' on the radio in the late 1970s then I don't know how I managed to miss it - cos I listened to a hell of a lot of radio in those days!