In Japan, there are various "Pokémon’s Day" based on the word "Pokémon's name" or the number of Pokedex.
（Such as Corsola's day…3/25, after the Japanese name: "Sanigo"→"san,nii,go"）
These are all created by fans, but some of them have become official.（Eevee's day…11/21 , Vulpix's day…6/5）
I'm Japanese, so please forgive me if I use weird English( -人-)