User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-6050823-20140107011913/@comment-4009941-20140110054236

Examples of creatures the guild already knew about before showing in game series.

Zinogre, Duram, Azuros,  Red Khezu, Jaggi, Rheneplos, Lagiacrus, Giginox, Delex, Ludroth, Lavasioth, Hypno, Yama, Elder Dragons like Kusha were being researched you could say during time of MH1, Baru(Somehow they knew it came from over seas so they knew that thing existed), Nargacuga seems to have been known about since MH1, Crabs, Black Diablos seems to have already been known before game appearance, Alatreon apparently, Jho aggression was already known by eating researchers, Amatsu was already known, and some monsters in MH4. The list is quite big and I did not get them all.

As for monsters known by legends in the series: Akantor, Ukanlos, Odei, Zeru, Abyssal and more.

The guild knows allot more than people give them credit. Also note that they have some of these deadly monsters like Fatalis and a Akantor in secret. The guild can be shady so its likely they have even more secrets.