One further identification, which I just found made in the recent Young Reader
edition of the book: the white-haired gentleman with the monocle, wearing a black jacket, standing to the left of the picture is the absolutely spelndidly named Édouard Cnapelinckx, a friend of Hergé and Hergée (his wife Germaine).
If the name seems vaguely
familiar, it may be because a rather striking picture by Hergé which came up for auction in the recent past, showing Tintin and Haddock on a beach carrying shells
, was originally a gift by the artist to M. Cnapelinckx on his fiftieth birthday.
I have also seen elsewhere an identification of the lady in the green dress, standing just to the right of M. Cnapelinckx as you move across the scene, as Ginette Van Melkebeke, wife of Jacques Van Melkebeke.
Several of these people are also said to be in the music hall scene of The Seven Crystal Balls
on p. 16, when Haddock makes his "bull-headed" appearance on stage: E.P. Jacobs is shown in the middle box on the left-hand side of the picture, together with a figure who, given his shock of hair, could be Jacques Van Melkebeke, although he has his back to us. In the foreground, to the right of the page, and reading right to left, we have the blonde head of Germaine, and then M. Cnapelinckx, and a lady who is said to be Manon Cnapelinckx, his wife.
More interestingly, M. Cnapelinckx actually seems to appear twice
, as if you look back to the box on the left, you will see a man sitting, bearing the same round head, fringe of hair and curved nose!
One last thing; M. Cnapelinckx was the manufacturer of the silk scarves produced by his company Mantérob, to mark the end of WWII which are mentioned in this thread
– and therefore was an early and perhaps un-sung hero of the appearance of Tintin in English (albeit under the pseudonym Tufty
Having found further information, it seems that the young man in the front row of the music-hall, sitting three seats in from the left and pointing at the stage, is Michel Regnier, known as "Greg"; if this is indeed the case, I think it might be possible that he is also the person I thought was Van Melkebeke in the box, as they look to be twins.