Clouds have been around for billions of years. The modern classification system was completed in 1951. Or was it? It seems absurd we haven't properly classified all the cloud types, but maybe.... A very strange type called the agitated wave cloud - or undulatus asperatus - has been proposed as a new "species" deserving addition to the cloud "zoo." This dramatic swirly/wavy formation wasn't even photographed officially until 2006. See here for dramatic pictures
When my daughter was in third grade, she pointed out cumulus clouds to me and said, "I'm just telling you this because they probably didn't know it when you were in school." She may not have been entirely wrong.