"Won't add up" <- check yourself the amount of eMule 0.30 users around. Now guess why it won't add up.
"Maybe there should be older line" <- yes, from 0.01 to 0.42e for eMule, from 1.0.0 to 2.0.0rc3 for aMule, from ... fro MlDonkey, lphant, eDonkey, cDonkey, jMule, Shareaza... Then next post you'd post here would be "why is aMule useing 89% of my CPU?"
"So there are 900 clients that are unknown but listed as emules" <- "Unknown" clients aren't counted in the "total" count.
Greetings.