TS4 Studio question

Hello, can you answer me, how difference is between "Career Tuning" and "Sim data"? Because. When i want to replace name of career level I must rewrite this: <T name="title">0x5AA4E1E4</T> in "Sim data", no rewrite it in Career tuning, but when I want to change example salary, it is vice versa, I must rewrite it in "Career Level Tuning", no in "Sim data". Despite the fact that the salary data are in both - Career tuning and Sim data. Why I can´t set salary or work days in Sim data, when, in Sim data are work days and salary written too? Or Why I can rewrite Career level title in "Career Tuning", only in "Sim Data"? Despite the fact that the name of career level are in both. Can you explain it to me? Thanks for help.