Grade - Salary Grade

Hello, all
I am coming with an issue in regard to grade of employees.The organisation I joined is marking employees under executive,serior exe,staff,asst.manager,manager and sr.manager.But what I noticed is that particular grade is not fixed with particular range of salary.for eg: few executives drawing more than asst manager again in some case asst manager more than manager, some sr.executives are drawing below executive range.After I joined I changed the grade and kept a salary range based on grade,such as:
Exe:10-15
Sr.Exe-15.5-20,in this way.
According to my knowledge,grade is based on experience and efficiency at times.
Want all of your view in regard to the same and the procedure I'm following is correct or not?

Additionally, I have one more question,that is,is staff a type of grade?

A grade for internal promotion shall bear reasonable relationship with the level of qualifications, skills, knowledge,responsibilities for which decisions to e made and the degree of value to business, expected from that role and finally experience. Here experience means exposure to handle the responsibilities efficiently but not years of service as sometimes it may denote only a number but not talent.Other experts may chip in with their contributions.as it is interesting.
B.Saikumar