by "available", is the page back in Soviets, or did you just mean it's in the various guide-books?
I meant more that the page - which was included in the facsimile editions in 1989 (both the brown cloth-covered special edition, and the white standard edition, with the picture of Tintin in Cossack costume) has now been back in circulation for thirty years; that's half the time that it was "missing", so it's hard to keep calling it "lost".
But as CaptainFatstock says correctly, it's a feature of the facsimiles only.
Confusingly, the introduction which explained its re-insertion as "97A" was still being included in the "standard" binding version, even when the page was taken out again - my Methuen copy talks about it, but it doesn't have it.
To further muddy the water, the facsimile page numbers begin on the second
page of the story (so "page 1" is the one with the anarchist saying "I think the dirty little bourgeois..."), while the Methuen book takes a different approach, numbering the page count from the front cover, so the first page of the story where Tintin boards the train (and the first to bear a number) is "page 4". The missing "missing page" would therefore in this case be "page 101A"...
In recent years, the French colour edition didn't get the page reinserted, but it was made available in colour as a separate numbered print with the initial copies of the deluxe version of the book.
my aunt's copy of Congo (which I think was a Casterman) has the endpapers with the Tintin figures
Sounds like she has the second, yellow, facsimile, with the illustration of the Model-T Ford inset on the front.