Abbreviated setlist in Pompei

Simon Brough from England wonders: "Why did Floyd not perform their entire setlist at Live in Pompei which at the time would have included Embryo and Fat Old Sun?  Similarly, why doesn't the re-issued CD of Ummagumma have the recorded Interstellar Overdrive on it?"

Live in Pompei was recorded from October 4th to the 7th, 1971 and the tracks were chosen as a representation of their live show at the time.  Coupled with the interview and Dark Side of the Moon footage, the film constituted a fairly conventional 81-ish minutes.  Embryo was not in contention for a release as the band were pissed off with Harvest Records for releasing a demo version of the track on the "Picnic" compilation.  Both Fat Old Sun and Embryo are very long songs and time limitations versus variety of material to make and interesting and balanced release are also necessary factors.  In concert faves at the time also included Atom Heart Mother and Cymbaline (at that point still).  So be thankful we were spared the full monty!  Ummagumma omitted Interstellar Overdrive because, it is said, the tapes of the track in question were disappointing.  That was the official reason.  John Peel had a 30-minute tape of Interstellar Overdrive recorded by the Floyd at Mothers until a thief added it to his collection.  John reported it was a marvelous performance, comparing it to the sound of dying galaxies.