I find it hard to believe that Siemens would intentionally make inferior tubes for Amperex, or vice versa. It’s an impossible concept. I have Valvos made by Amperex, and British Brimars made for German Lorenz with the German military hawk symbol on them. They work great.
Of course, we want our tubes to have matching codes, and names, but these days it’s becoming increasingly difficult to find. However, if they were made at the same factory within, say, a couple of years and have the same construction, I wouldn’t mind buying them even if they have different labels—as long as they’re matched, of course. In my experience, the sound will be indistinguishable from the originals.