Why do old tubes sound better than current tubes?

Viridian, we found something we can agree on; I think. New tubes do not even compare to NOS tubes. NOS tubes can take gear to another level. Let me be specific; I am referring to preamp tubes, those are the one's I have had experience with.

I have a rather LARGE collection of NOS and "pulled" tubes both preamp and power tubes bought most in the 90's. I 100% agree w/ orpheus & Virdian. I originally collected vintage guitar amps from the 60's (mostly Marshalls) before I got into i-Fi again. In my experience ANY new tube does NOT compare w/ vintage tubes,period! Now I'm just talking preamp tubes. I will attest to the fact that when it comes to KT88 and Kt66 tubes some of the new ones beat out my vintage ones. I must stress that I'm comparing them to vintage USED.
When it comes to NOS and even used 6L6's/5881's, El 84's, and EL 34's..... NO COMPARISON! the vintage win! Especially true w/ EL 34 mullards and telefunkens. I would not even "think" to put in ANY of the new variants available when it comes to them. My 02 cents...

Viridian, Opheus10, Tjnif, others...

Regarding some of the more commonly used preamp tubes, do you find that "joe's tube lore" remains a valid tool for winnowing/choosing vintage pulls etc when preparing to do tube rolling?

Jim

Nostalgia?