HTupolev

It's true that I'm not familiar with the tire clearance of literally every single model of bicycle ever made. I wasn't claiming that nobody had ever made a super-tight-clearance bicycle in the 60s or 70s; I was saying that it was typical for there to be wider clearance.

Also, I just looked up photos of a 1978 Benotto 3000, and it's not obvious what about its geometry would dictate a limit of 23mm. The tires it's wearing in those images are about 23mm wide judging by the frontal shot. The fork and rear brake bridge clearly have room for far more, and the chainstay bridge is also positioned very high out from the tire. The only thing that might be preventing a much larger tire from being installed is the chainstay profile, which is hard to make out in the shots... but even if it is the limiting factor, you wouldn't really need to alter the bike's "geometry" to widen that up somewhat.

It's also bizarre that you're acting like I should have known that "world champion geometry" refers to the geometry of a single model of bicycle that Francesco Moser happened to ride to the rainbow stripes in the later years of the period being discussed. A whole lot of people rode bikes that could readily fit 28s or bigger to world championships in the 60s and 70s.