Employment Reference Letter

[lavneet]

Should the letter include all the positions I held at the company?
I worked as 'Software Engineer Trainee' for an year and 'Software Engineer' for the rest of my tenure.
Since the salary was revised every year, which salary should be included in the letter?

Now that I work as Data Analyst which is different NOC, is it required to include proof of the current employment?
I already have 3+ years of experience as Software Engineer

Thanks,
Lavneet