The difference betwen the '68 "Circle" and '78 "Circle" is actually about 9 years. Strictly speaking of when they were recorded,1968's was recorded in September and the new version was recorded sometime between Aug. and November of 1977.
I went to this link to get my answer but also if you'e interestd in Gorodn's complete singles output (Canadian & American),as well as petty much his whole life story check out this link:
http://en.wikipedia.org/wiki/Gordon_Lightfoot.
Also,under the singles list,I edited in a notation about two of Gordon's earl 70s singles that didn't make the American Hot 100. I felt it was worth mentioning,since they didn't.
Happy 40th Anniversary this month to "Did She Mention My Name" by the way.