From the release of the game, until now, there were many changes to Pokémon Eggs distances and their hatchlings. Usually, changes occur when a new set of Pokémon is released. The first observed changes to egg distances occurred in late summer of 2016. There were also some temporary changes of eggs pool during the events.
For the list of current available Pokémon in eggs, see List of Pokémon eggs hatchlings.