It is true he used occasionally focal lenghts outside the 50mm, as is true though he used the 50mm predominantly. Ishu Patel has a vivid recollection of his meeting with Cartier-Bresson and reports that he had with him a 35mm lens alongside his standard equipment: "...From his suitcase he pulled out a small nylon bag containing a note book, a spare Leica body wrapped in a handkerchief, and a 35 mm wide-angle lens also wrapped in a handkerchief..." Other people report that he wasn't happy using other focal lengths. In a recent interview, Koudelka said "As Henri started, he finished". (His discussion at that point was about photographic vision and how that depends also on equipment, so, presumably, he was also commenting on Cartier-Bresson's camera/lens preference.) John Brinnin, who accompanied him in his abortive US trip/project, also reported Cartier-Bresson's dismay for the fact the scenery suited better the 35mm than his preferred 50mm.
A couple of examples: Au Bord de la Marne seems to me to be a photo taken with a 35mm. The date was 1939 so the lens was probably an early Elmar 35/3.5. En Brie, on the other hand, looks to me made with a 90mm or longer, possibly the Elmar 90/2.8. Bearing in mind the relatively scarce use he made of the 35mm, I think it unlikely he ever used seriously a 28mm or wider.
PS. ^^Thank you for the link to Cartier-Bresson's Hyeres, 1932 photo and its present-day reconstruction. The compression of space seems near indistinguishable in the two photos. Had he used a 35mm the difference would be more prominent. Perhaps differences in framing could be accounted by difference in height in the older and current staircases. IMO Cartier-Bresson must had used a 50mm for that photo.
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