Are multiple reference letters required, if Bosses and Designations changed multiple times?

[ChessWriter]

Hi,
I haven't found the answer to this despite spending hours upon hours scouring the internet.

I was employed in an organization for 2.5 years. I began there as a Clinical Resource Consultant and was reporting to Regional Sales Manager.

• At 9 months, in an organizational restructuring, my boss changed but the job title remained the same. I began reporting to National Medical Affairs Head but my designation remained Clinical Resource Consultant.
• At 12 months my salary increased after an appraisal.
• At 14 months, my job title was changed to Medical Affairs Manager, I kept reporting to the National Medical Affairs Head. At this point, my salary structure was changed but the overall salary amount remained the same i.e. Sales Incentive was changed Local performance variable pay.
• At 24 months my salary was increased again after an appraisal
• At 30 months I left the organization

I am going to take a letter of reference from my Boss. My questions are:

1. If I take a letter of reference from my boss, do I need 2 separate letters of reference for my 2 different job title, from both my bosses?
2. In the first designation, I had a different boss at the beginning and the end of it. Which one should I get a letter from?
3. Which salary should be mentioned on the letter, the one I had at the beginning of a role, or the one that I ended with?

* Getting a letter of reference from HR isn't an option because they won't give it in any template except their officially approved one, which wouldn't meet the requirements for Canada Express Entry.