>>14203145OP's list aside, I've stated now in multiple threads that Goomy and Sliggoo are 19 and 20 in the Mountain dex, and are exclusive to the Mountain dex. 21 is filled up in the Coastal dex, not the Mountain dex.
People are mixing the dexes up willy nilly and making false assumptions. We don't know if Sliggoo has another evo yet, and we won't know until someone leaks it or someone leaks a completed portion of the Mountain dex or a high leveled unevolved Sliggoo.