I don’t mean to derail this in any way but wanted to add my experience. In the pursuit of better sound we search out tubes,sometimes based on some thing we read like "Joe’s tube lore".Why Not ? It’s a fun and informative read. But these and similar reviews/comparisons, although meticulously done, might only have used a single example of a given tube. Someone like Joe, came to these conclusions within the context of his system, preferences, and gear that was posted on the asylum 25 year ago. Much has changed since then including equipment and tube supply.
Tubes can vary, time and usage takes it’s toll if the tube is not New Old Stock. I trust the opinions of the best tube resellers like Brent Jesse. They have experience with multiple examples of a given tube over time and have a reputation/business to maintain..
One can generalize that performance will be similar over many years of a tube’s run if the internals look the same and that may be more important than getting stuck on a specific date.
I’ve bought supposed "Holy Grail" tubes that have "underperformed" my expectations.
I’ve bought tubes that are not the same date codes as the recommended ones that sound as good because they are the identical construction. Buying old tubes is a bit of mine field but So worth it when you do find the gems.
Case in point I recently bought some Matsushita tubes.When Mullard closed down Matsushitu bought the tooling from them and continued to make them in the meticulous way the Japanese do. The resulting tube is sonically equal to the equivalent Mullards I have and were a fraction of the price and easy to find New Old Stock