It is related to alpha access because CIG created it in order to limit the access to alpha by people that payed for it. Why else would you have a public test environment for a public test environment. NVM that the PTU is in fact an alpha build that is just restricted.
Like I said CIG did not return the alpha access worth, because they didn't refund any money.
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So we have assumed that the UEE number was the number of payed accounts, turns out that might not be true. According to Ben its the number of add on ships backers have purchased.
https://forums.robertsspaceindustries.com/discussion/comment/3194283/#Comment_3194283
But its Ben so we can't believe a word he says. Is kind of funny how the community manager (well used to be, or is now since they fired that person), is someone that you can't believe what they say, as its been shown he just makes things up. Well that's open development for you, hahahaha.
Anyway, so according to Disco Lando, the UEE number is also just the number of ships sold.