It's a incremental process. You model a certain experimental ("discovery") thing, then you implement it then you analyses the result then you change the model

It's a incremental process. You model a certain experimental ("discovery") thing, then you implement it then you analyses the result then you change the model etc. And sure in many cases in practice people might not skip the modeling but don't properly write it down in any later one usable way. Especially during initial experimental discovery phases. Which isn't good. But understandable and can be fully ok. Honestly especially for boring simple web API's this is pretty common. It's just important to know when to stop ;=)