Let me be, perhaps, a little clearer in explaining what I'm thinking. I think it takes years of experience to really know your way around vintage tubes. Without that experience we're relying on others to guide the way. Isn't that one of the purposes of this Forum? To share our experience?
It is.
My experience is, yes tubes do sound different. It should be obvious they are not all the same, if only for the simple fact sometimes one blows out while another one of the same type and brand and age runs for years. They all pass the same QA measurement tests so that should tell you all you need to know about the efficacy of measurements. This much is all obvious as can be and so it remains a mystery why anyone still wonders about such things.
This does not mean there are no physical properties might that account for the superior performance of certain tubes. The most experienced and knowledgeable man I know on the subject, Raven Audio's Dave Thompson, told me he heard from an engineer who worked at the factory where some of his most cherished tubes were made that the equipment used then pulled a vacuum 20% greater than today.
So there are reasons, and let me know the next time you see the inches of mercury vacuum stat on a tube.
Even then I would have to say that is just one on a very long list of factors. Tubes are a connosseur's game. Reliable information is so hard to come by that I gave up years ago. Until learning about Raven and Dave. Now thanks to Dave I know whatever I buy will indeed be well worth the extra. Just last night I swapped out a TungSol and moved some of Dave's around to the rows he recommended, and immediately experienced extension, nuance, and real live emotion like it was a whole new amp.
These are tubes collected from a lifetime of searching and comparing. This transforms tube rolling from a crapshoot to just about the easiest and most rewarding thing around. All you have to do is buy a Raven amp. The stock of these NOS wonders is limited, and when they are gone they are gone. He only sells within the Raven family. So there you go.