EntityClass["AdministrativeDivision", "States"] is not a valid EntityClass. You can find a list of valid entity classes by running EntityClassList and InputForm to see the actual InputForms of the entities.
Is there a valid EntityClass given by EntityClassList that isn't working for you?
There is no Interpreter for EntityClasses. I'm not sure that one would be helpful. They represent something kinda more arbitrary than Entities or EntityProperties. They're just a list of what curated lists already exist and are rarely ever complete in some way, which you are unlikely to be able to guess without running EntityList.
