Vintage Italian tubular steel stacking chair ID  

I'm stumped, so posting for the first time to this forum (which I've long enjoyed as just a casual reader).  My partner recently acquired this pair of vintage (80s?) leather upholstered tubular steel stacking chairs, one of which retains a "Made in Italy" sticker on the underside of the seat. One notable feature is the "stacking ring" welded to each of the rear legs, which secures the chairs' legs when stacked (a design element I've never seen before).  My partner's instincts tell him these chairs are the work of a notable designer, but despite much googling have been unable to find out anything about them. We'd welcome any comments, clues, or definitive pronouncements. Thanks!
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