Now Reg, that's not your way of saying that TYA was Alvin Lee, is it?
Nearly correct Alan, nearly. That photo was used (many times) as a 'teaser' advertising campaign in 1973, for 'Recorded Live'. Reg says 'teaser campaign', as the advert was just that photo, with no other info apart from just the words 'Watch it!'. It was only nearer the date of the release that more info about what was being advertised also appeared.
And in a controversial note Reg could point out that, ironically, if you really did want 'The Best of Alvin Lee' it is 'Recorded Live' that you should be buying.
No. It's a belief that that was when they were all at their best. (Certainly live, anyway.) Seasoned, without being stale. Mature performers, although still with the energy of young men still in their twenties. Masters of their craft. At their performing peak. Etc.