On October 31, 2019, datamine group PokeMiners discovered a live update made to the Pokemon GO code that included assets. This update did not change anything in the game, but behind the scenes in the code, there may be something going on with this collection of Pokemon.
The list seems to refer to image assets according to the file naming convention. The first four numbers refer to the Pokedex ID number, while the second refers to a form such as Alolan Sandshrew(pm0027_61).
The most interesting form listed here is for Weezing(pm0110_31), a Pokemon that doesn't have any currently available forms, but does have its recently announced Galarian form.
See below for the full list.
Articuno is another oddball on this list as the only Legendary to be found.
This could be related to the "A Colossal Discovery" event we have arriving on November 2nd, 2019 at 11 AM. We have not received any details on the content of the event, only that it will include 10 free Raid Passes, a Unova Stone, and Regigigas.