Yeah, PapaGator -- there are minor differences, but when the difference is one or two notes within the same chord pattern it becomes almost academic to call them different, don't you think? It's like the old C-Am-F-G7 thing. Many years ago I used to do a thing in my performance that used that chord pattern and I did a medley of about six or seven songs without breaking the rotation. I don't even remember now what all the songs were, but it wouldn't be hard to work it up again.
There are always little squiggles in the tunes, but often they can be attributed to how you stretch the words over the music. It'sof phrasing, not really tune differences. And, of course, there are songs which are, as you say, very similar without being the same. Sometimes the differences are not at all clear.