Groove Tubes (now owned by Fender), Ruby Tubes, Mesa Boogie, TAD (and may other makes) don't make valves. They test and reband valves made by other manufacturers.
Some of the valves they sell are exclusive them, ie they are made only for that company.
As far as I know there are only 4 factories still mass producing valves for the guitar market:
JJ Electronics in Czech Republic
Saratov plant in Russia (makes all EH, Mullard, Tungsol, S-Logo Svetlana, Genelux, Sovtek valves).
Svetlana plant in St. Petersburg (=C=)
Shuguang factory in China (although there could be other Chinese factories, can't really tell what's going on there, although as the CRT is now virtually obsolete I expect there aren't many factories with vacuum tube capabilities).
The Ei factory in Serbia may be making valves again, I don't know, but they did go out of production.
As you can see, there isn't really a great selection of valve manufacturers, despite a multitude of brands. There is little point buying a JJ-6L6 rebranded from Groove Tubes at greater cost than you could buy the same valve from say Hotrox branded as a JJ-6L6. So unless you really want a valve that is proprietary to a rebrander, I would go with a reputable vendor and save money.
For what it's worth I've had very good results with JJ-6L6s (so I'm very pleased they have sorted the pins out on them — they now use correctly sized tapered pins), although I have had a couple of new tested valves flash over in amps with B+ over > 500 V. I use =C= 6L6s in may main concert amp though!
