PS FRM: There's a different release called 'The Fillmore Concerts' in which the two lead guitars are mixed a little less 'hot', probably a more accurate representation of how it sounded at the concert but takes some getting used to when you've been listening to the album for 40+ years. It has material from both nights. 'Elizabeth Reed' on that release is a splice job between two performances to combine the 'best' parts, a practice that I have misgivings about.
Back in my vinyl-spinning days, I had the Nautilus half-speed-mastered version of Fillmore East, which sounded very good.
Two personal notes: I had a friend who was at these shows and was always jealous of that. I also had a chance to see the Allmans on 10/17/71 in what was as far as I know the last show featuring the original lineup, a double bill with B.B. King at Painter's Mill in Owings Mills, MD. They jammed together
And where was I? I had free tickets to John Denver, which was good (it was before he went commercial, just a three piece acoustic group), but if I had a time machine I'd go back and hear the Allmans. (Frank Zappa was at the Lyric Theatre and the last game of the World Series that day too- busy day in Baltimore.)