I agree this was a lovely puzzle. I was 12 in London in 1969 so wasn't aware of 10 25 at the time, but there are a couple of very good films or documentaries (either of performances of discussion of the event) and of course songs (eg CSNY and JM) to tell us why it was important.
I'm sorry Paul couldn't find space for the first of those, or for the wonderful JC's classic performance, but a very enjoyable puzzle and reminder of some good acts.
I'm sure I'm being stupid but scratching my head in the NW (I worked out fairly early that 11, 2, 3 should be 11, 3, 2). I can't figure out 1d, 8a or 12a, any hints would be appreciated please? I'm also puzzled by 20a, I've got two answers that fit (different choices of first word) but I cannot parse either.
Thanks to Paul and to friends here!