Vintage lenses, are generally considered vintage if they were made for cameras that used film. These items were made with production processes not comparable with the current ones.
Most of the vintage lenses on the market today. I’m referring to lenses that can be used (in good order and fully functional) adapted to modern digital cameras. Were made in the period following the II° World War, until the early 90s.
The lenses to which I’m mentioning for these notes are lenses produced from the end of the 1950s to the early 1990s.
The production quality standards were obviously very different from the current ones. Both for the optics part and for the mechanical part.
The project, and the preventive study, was certainly not carried out with modern computers and software, for the calculations necessary for the realization, as is the case today. All the design and preparation for mechanical and optical production was essentially hand-made at its origins, and progressively improving over the years.
The same production process, although generally of good if not excellent quality, was practically almost exclusively to specialized workers, who obviously could not guarantee a production standard or uniformity in the realization of the pieces.
It’s also true that progress since the years following the II° World War, in particular since the 1950s. Progressively introduced ever better designs and creations. Using ever better and more sophisticated machinery and tools. It’s certainly far, really far from what is achieved today for modern photographic lenses.
In conclusion, the same lens, the same model, and the same manufacturer. MAY have qualitative differences that are sometimes quite evident between them. It is not a rule, mind you … but it can happen. I personally tested two SAME lenses with different photographic results under the same photographic shooting conditions.