When using the terms “left” and “right”, I shall use the convention of speaking from the viewpoint of the observer.
The Wikipedia entry actually shows not only the 26 people who can be seen relatively clearly, but also three more who are cut off at the left, but who were clearly present at the shoot. These are Clive Bunker, the drummer with Jethro Tull, Richard Thompson of Fairport Convention, of whom can be seen a bit of hair, and Chris Mercer (?) of whom a little more can be seen.
It can be observed, nevertheless, that the composer of the photo, being someone from Hipgnosis, has shown great skill in setting and framing the picture.