Tubes - Sylvania 12ax7 vs 5751 3 mica blackplates

I am new to tubes and am wondering, "Are NOS Sylvania 12ax7 triple mica black plate tubes identical in every way to the famed Sylvania Gold Brand 5751 triple mica black plates?" One source claims that if the 12ax7's have the same gain, THEY ARE 5751's even though the boxes and labelling on the tubes say 12ax7. Can anyone confirm or comment on this? Is it possible that Sylvania "mislabelled" tubes? I am curious if there are differences in the construction, quality, value (cost) and most importantly sound.
5751 have 70% of the gain of the 12AX7s, or less gain than 12AX7s. Sylvania made both type of tubes. Lots of articles out there will confirm this.

You may want to try the link re: Joe's Tube Lore for more info on this and other questions you aked about the two tube types.

I note the author of the article reports in it, concerning the Sylvania 12AX7s,
The rest of the pack - the Sylvania/ Phillips, GE, RCAs, etc.. are even worse.

The author of the article loves the Sylvania 5751 triple mica blackplates in its various guises (less so the Sylvania 5751 triple mice greyplates), but go ahead and read to article to find out more.

I've got a NOS pair of Sylvania Sylvania Gold Label JHS 5751WA triple mica blackplates currently in my Jolida JD-100, and another unused back-up pair of NIB Sylvania Yellow Label JHS 5751WA triple mica blackplates [1956 date labels] (these are the same tubes, as the article will point out), and couldn't be happier with the pair currently in use in my system. Happy tube rolling, and watch your wallet!
I have an ASL MG HeadDT headphone amp. I had picked up 2 Sylvania 5751 tubes to replace the center ECC83. When I replace the ECC83 with either 5751, I get a very loud buzz in the right channel. I've heard of other users using 5751s in their ASL. Did I buy 2 bad tubes or is there something I'm missing?