It seems to me, you, peolpe, overloocking one substantional circumstance in you research regarding Brand New members. Thing is, you often can`t register and not get a ban at once even from you own IP adress, espesially if you are a TOR user. But sometimes (as was in my case) you just randomly get some point of evel (like, about 10 or smth) and can`t post a thing till you pay some fee, less than comission. So, naturally most of new users don`t know about IP ban feature untill they try to register and in most cases, unsuccessfully. So, here comes another acc or two or three, and most of them are pictured green in that diagram. They`re just dead accounts, nobody will ever post from `em, that`s why this number of Brand News.
If you want real numbers, you should get a quantity of IP banned accs and exclude such ones from calculations.