What happens when grades are synchronized?

The profile options to default or enforce valid grades are ignored when grades are synchronized.

If multiple valid grades exist at the position, then you can select an appropriate grade in the assignment. If you hire a person into the position, which has an entry grade specified, then the entry grade will be the default value in case of multiple valid grades.

If the assignment has both position and job, then synchronization from the position always takes precedence and the values at the job will be ignored. Let's say you haven't defined any valid grades for the position. However, valid grades are defined for the job and the assignment has a position. Then any valid grades for the job are ignored.