From my experience this is NOT true. You have to at kill at least 1 of EACH subspieces (class specific not included in most cases) of the beast found on that world. Any variation on the name is included. If you miss any 1 of them, it will not unlock.

9/30 and just got my email. I was able to log in as soon as I saw late September people start to get in, email arrived about 15 minutes later. So if you haven't received the email, there is still hope Looks like all of September has now made it!