Yeah I agree. There's a lot more needed than just the User Story, one way I'm thinking about it is that the "core" is deliverable business value, and the "shell

Yeah I agree. There's a lot more needed than just the User Story, one way I'm thinking about it is that the "core" is deliverable business value, and the "shells" are context required for fine-grained details. There will likely need to be a step to verify against the acceptance criteria. I hope to back up this hypothesis with actual data and experiments!