When is a Pokemon determined to be a ditto in Pokemon Go? When they spawn into the game or after you catch them?

Question

As you people who still play Pokemon Go know that Ditto is now available in Pokemon Go. I want to ask if there is a really low chance for a Pokemon to become a ditto, or is the Pokemon disguised as ditto pre-determined?

Answer 1

The Pokemon disguised as ditto is already pre-determined. I know this because my cousin and I both caught the exact same Rattata, and they both turned into a Ditto with the same ivs and CP.