There are two possible explanations for this (or three if you believe in spontaneous generation).
They were extinct in the wild but still alive in captivity and then reintroduced into the wild.
They were in the wild but no one came across them, that's to say they were very endangered, and thus there were so few that none were seen
They spontainiosly came into existence, this is known as "spontaneos generation" and was a thing a long time ago
rocks and weathering-matching
the answer would be knowledge about cars!
happened to the Black Rhino