DMM API is more of a loose contract. In one instance something will work, but under specific use-cases, it behaves differently. There are lots of parameters they accept, but no clear reason as to why they need it, or when. Sometimes you can omit parameters, sometimes it is mandatory. Behaviour is also random. In some cases, an API will behave one way, but in another, it will do something different. There's no way to know since every title has the potential to behave differently. You just have to do lots of auto-detection and retries to see what works and what doesn't and dynamically handle each use-case as it comes up.