In this case "what the server produces" was already defined and I was not given a mandate to change it prior to v1.0. Also, the server implementation was a bit

In this case "what the server produces" was already defined and I was not given a mandate to change it prior to v1.0. Also, the server implementation was a bit messy and mostly undocumented. So I worked "backwards" in the sense that I put myself in the perspective of a consumer of the information it serves and then documented the server's behavior with OpenAPI. Certainly, in the process I made much reference to the Python code used to implement the server's endpoints, but some of the endpoints' quirks were discovered in the process of precisely describing (with OpenAPI) their inputs and outputs.