My take on the "sound" of different manufacturered tubes, whether NOS or current production is that each brand has a "house" sound. For example, the famous NOS Mullard Square getter, 1959 ECC83, known for it's amazing musicality( especially in the midrange) and warmth might be a little too warm in some circuits. I prefer in my 1959 Pilot 402 receiver( bedroom system) an early 60's Siemens double post ECC83, only because it is a little more neutral with better extensions and it seems to compliment the Siemens E84L power tubes. Yet in my VAC Monoblocks, I am using an inexpensive($6.00) stock Philips 12au7aw( 1989) tube because it sounds the best as the driver tube for my current production Chinese-made Shuguang KT88-98 power tubes, which are an amazing power tube. The Shuguang company has come up with a marvelous power tube with this new KT88-98. And they're priced very reasonably as well. I've read that the solid plate version might be better in some respects) Perhaps tube-rolling can be associated with fine-tuning the tone, but there is much more than that taking place. As a musician, besides tone, which is very critical, I look for timbre, proper soundstage, imaging, extended yet refined and delicate highs, natural midranges( palpable voices, accurate portrayal of a well-miked piano) and midbass and subterranean bass that is accurate without being bloated. I have listened to a number of excellently tested preamp tubes that have a difficult time in portraying accurate and realistic bass. Of course, I could always get a fancy equalizer like Carlos to "force" that bass to be accurate. But, in my humble opinion, any equalizer in the circuit, as Rhyno mentioned, will in some way affect the signal to degrade the purity of the recorded sound. I suppose it's a matter of trade-offs, but I'd rather fine tune my room acoustics without the use of an in-line equalizer. Any true red-blooded audiophile has my blessings in finding the right tube to roll if he pleases. Fortunately, the designer of my VAC amp, Kevin Hayes, is not only a brilliant engineer, but has a very good ear as well and his factory tubes are "voiced" perfectly to suit my discerning ears. I had to learn the hard way with Mucho $$$ in tube rolling.
