The vagaries of tubes LoL. Like I said in previous posts, all of these tubes are selected for low noise/microphonics and high(ish) gain, there's also matched triodes etc. In the end they all sound different. Most are re-badged something (Boogie, GT, Ruby et al), there are only a limited number of tube manufactures, Tesla (JJs, Slovakia), New Sensor (made in Reflector Factory Russia and they make a bunch of other brands (e.g. Tung Sol etc), Chinese Tubes (quite a few, TADs? Shugung whatever). In the end IMO, short or long plate matters (I've found that long plates are more 3D (doesn't suit everyone though)). We all react differently to our tubes (depends so much on how you play), it makes more sense to me to compare them like guitar strings as they are all low noise, high gain blah blah, well how do they sound, in my preamp, with the way I play and which ones to avoid (e.g. Sovtecks, EVs).
So what I'm getting at here is that the various tube testers (re-sellers/branders (Boogie, GT, Ruby, Bugera etc)) are just concerned with low noise/micophonics high gain with little emphasis on "how the f&ck" do they sound (which BTW will vary in every circuit). I suppose at least we are trying to compare the different sounds in the same preamps but then playing style is very important.