Friend of mine bought WE 211 from Penta labs as well.....I wonder if his tubes were also B stock and like Spareribs, wonder about the quality issues.. $300 a pair seemed like a good deal.........or not likely?
Probably not but I can tell you from experience that they will likely develop problems over time. I had a set and they started to emit a popping sound after a short time. The tube was repleaced by the seller and the new one started popping too. Since you already own them I wish you luck but for my money I would never buy B stock tubes again.
I just emailed another tube dealer at Allegrosound.com who sells both WE 300B tubes with and without serial numbers. The ones with no serial numbers are cheaper. According to Rick at Allegrosound.com, there are no sonic differences.
My feeling is that the tubes with no serial numbers were not tested by WE but if they were tested by another company and tests OK, I assume the tubes are fine.
But it's just my guess. I think WE sold a bunch of non serial numbered tubes for economical reasons, which would be fine as long as most of them are legitimate.
Again, this is just my educated guess.