I find your comment interesting. A couple of years ago I began selling-off my tube collection as I no longer needed them having switched to solid state. I went to list three matched pairs plus a single Tungsram 7DJ8/PCC88 that I’d purchased from Tubemonger: March, 1971 production. Anyway, I didn’t list them because I had a Post-It note on the batch that some of them had become noisy. This was within the first few hundred hours of use.
Those are two reputable sellers, guess we didn’t fare well with them in this particular case.