Thanks Art! You've got me beat on concerts by a longshot. Yes, thanks to the internet, I've been able to tap into all sorts of rarities from the Stones online like that one. I especially like hearing different versions of a song, different lyrics and mixes that eventually lead to the album version. Slave from Tattoo You is a great example of one like that.
I highly recommend the reissue box sets of Exile, Sticky Fingers, and Get Your YaYas Out as well.
Here's the alternate version of Can't You Hear Me Knockin' that was included in Sticky Fingers:
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