I am not a technician or engineer or anything of the sort. So, this is all an educated guess on my part. I wonder if the JJ 6V6S was another "military" tube that was found to work well in a 6V6 circuit? I don't know when it was designed, but given that the factory is in a former communist country...
I don't see it as a reissue 6V6 or anything of the sort; I see them like I see Sovtek 5881WXTs - cheap, sturdy tubes that take a lot of punishment. I like that they won't stress the heater winding like a 6L6 but they take crazy (for a 6V6) voltages. I would ask if you're willing to torture-test them, go for it & let us know what you find! I'm sure they have tested the parameters on their data sheets, but verification doesn't hurt.
I'll leave it to the experts for anything else.