They showed 3 or 4 and then they went off and said Giant River Otters, Capybara's and the pink Amazon fresh water dolphin all three species having been known for decades if not a centuries.
These species are being discovered because the Amazonian Rainforest is being logged and burnt into non-existence, and if there's no habitat these "new species" are unlikely to survive a decade or two.
Extinction is rarely a clearly defined event, like the end of the Dodo on Mauritius. Extinction in dense rainforest-like environments can have to do with reduction of population so they are no longer seen. But there's no evidence that these species have survived, so they are written in as extinct.
Another example is the Ivory Billed Woodpecker being found again after 60 years in the Wildlife Refuge in Alabama. We have no clue as to how many Ivory Billed Woodpeckers there are because they are so rare, only one has been seen in 60 years despite Cornell's surveys over the space of many years.