What are the encounter rates for Stakataka/Blacephalon in USUM?

Question

Iirc they are limited like 2 you can capture per game, but what are the encounter rates while they are still present for you to catch?

Comments

I thought it was 3 a game

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Me too and that's what I originally had, but I saw 2 in another question so I changed it. It's either 2 or 3 but I don't know if the amount left influences anything.

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If you have a Repel active and a leading Pokemon between level 55 and 59, they will amount to 100% of eligible encounters.

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I'm not trying to get a 100% encounter rate, I want to know the rate of a non guaranteed encounter.