Where did you get the data? Are they public?
I literally checked which profiles have "Never" as their last active date, like I mentioned in the OP. I don't know if that's entirely accurate but it seems unlikely that so many users would just register and never login for some other reason.
This will not predict if someone has to pay a fee. When you sign up for an account, you will get a message saying there was a "cookie error" and that if you just signed up, you need to login. At this point, there is no indication you need to pay a fee, and the profile last active date is "never". Once you login, there will be a message at the top of the page that you are unable to post with a link to the proxyban page that tells you how much you need to pay to get unproxybanned; once you login, your profile will no longer indicate your last active date is "never".
A profile indicating they have "never" been active means the person has never logged into their account, and does not know if they need to pay an evil fee or not.
I just confirmed the above procedure a minute ago and the above is correct.