The concern that I see concerning your salary grade is that if you were offered a certain salary and agreed to it where you received this salary, there does not seem to be a basis for you four (4) years after the fact to now complain about it for the very first time.However, in an abundance of caution, you should bring the issue up to your immediate supervisor since you work in the human relations department and get your concerns clarified. Nothing ventured is nothing gained.