I haven’t used a 5670 so I can not comment on your question if there’s a sound difference between JAN/2C51 marked WE396 to one just marked WE396 . If you are unaware of it, there was an Orchid DAC thread that possibly has some discussion about that; if not it will afford you identification of some members that own the Orchid that you can possibly pm to get some direct insights.
" I realize that audible variations may be hard to hear at the DAC level so there’s that. " I have a Modwright Elyse DAC in my 2nd system; I can tell the sonic difference between Phillips, Siemens and Mazda 6922s in that DAC . You do have some options between variants and brands 5670, 2C51, 396A, 6385, 6CC42, 6854, 6N3, 6854, CV2575, CV4013, CV5894, CV8247, CV2381
I have not found glass warping to be "common" with small signal tubes.
" I realize that audible variations may be hard to hear at the DAC level so there’s that. " I have a Modwright Elyse DAC in my 2nd system; I can tell the sonic difference between Phillips, Siemens and Mazda 6922s in that DAC . You do have some options between variants and brands 5670, 2C51, 396A, 6385, 6CC42, 6854, 6N3, 6854, CV2575, CV4013, CV5894, CV8247, CV2381
I have not found glass warping to be "common" with small signal tubes.