The things which must be included are job title, duties and responsibilities, job status (if current job), dates worked for the company, number of work hours per week and annual salary plus benefits.
Salaries keep changing, and need not to be the same, every year so I was thinking to mention the salaries of all the years independently. If your NOC is same, most of the must be included things are same as well. Some things like salaries, which were different, can be explained for each year.
I know that you are aware but read it once more.
In the last 10 years, how many total years of foreign skilled work experience do you have?
It must have been paid, full-time (or an equal amount in part-time), and in only one occupation (NOC skill type 0, A or B).
So basically there are three thing; paid, duration, and NOC (duties and employment requirements)
A reference letter, itself, is proof of your work experience, salaries, duties, full-time or part-time and so on..It is given by an employer who takes the responsibility of your work experience.
If you are not satisfied, do more research as this a mandatory document and we have to be very careful.
Suraj