To me a rare song is something the band has played live less than 10 times EVER.
Songs that qualify:
i want you
if I was your mother
fear
cadillac man
i wanna take you higher
sylvia's mother
here comes the sun
bridge over troubled water
freebird

In my opinion a song isn't rare because it is a new version or the only time played on a certain tour.

I wonder how many Rare songs they have played I am sure it is more than 20, maybe more than 50.

What rare live songs can you add to the list?
Dave