I don't know that there's any definite consensus on this. Personally, I consider "vintage blacks" to be a misnomer. Both sets of "vintage" black switches that I have felt indistinguishable overall from multiple sets of more modern black switches from various boards I have around.
What makes the most sense to me is that Cherry probably retools every few years, and individual batches, regardless of tooling condition, may somehow come out better or worse than others that come before or after. I would seriously not be surprised if this "vintage black" thing all came out of some deal somebody found on a stockpile of identical boards from the 1980s with MX black switches and all of the boards in that batch just so happened to feel better than expected when everybody bought them up.