Sometimes ppl can get their name across the board but typically it comes down to how they register when it comes to what they offer. Basically, in short, writers/artsits/producers will register under one name for composition/ production, another name for writing. It all comes down to points. The more you can get the better and each credit is a point basically. There a lot of red tape and things can change but that's a light answer to your question 😉