This article has been updated. My thanks to Snapdragon133 and Crow-Cat for review.
The IUCN status was determined by the Cryptid Specialist Group at the IUCN. For obvious reasons, they do not release their work to the general public, though it's easily available for the anomalous community. Despite the fact that the IUCN is the sort of international NGO that fits with the Council of 108, they're not part of it because the Coalition never bothered informing them of anomalies. So they discovered anomalies separately in the 1960s, though individual researchers knew about them beforehand. By the time the Coalition finally approached them they'd known for years, and weren't particularly keen on attaching themselves to another organization.
They're left alone by the major anomalies players largely because of apathy.
The species is no longer called the Nigerian lava cat because, as it turns out, all the volcanoes in Nigeria are extinct. Whoops. They're still originally from the region, it's just by the time anyone was around giving them an English name they were long gone from the area.
The lack of clinical tone, despite this being a scientific report, is deliberate. It differentiates Legacy from the SCP Foundation and helps link them tonally to the Serpent's Hand (which they have open links to). While Legacy is more science focused than the Hand generally is, they're culturally pretty similar (and, given the Hand's lack of formal organization, not totally separate), so their scientists generally do not bother with the scientific tone in these sorts of reports.
I'm also trying to pull Legacy a little away from being focused on animal rehabilitation and rescue and more on in-suita conservation in this work. That's an unoccupied niche and I'm eventually hoping to establish them as a GoI both here and on the SCP Foundation so trying to cement them in that role will be useful.