Not sure if I can address these accurately but here is what I think (have personally done):
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If company A had multiple promotions, you can state the latest one and its fine, what matters is what is outlined in the ONE experience letter that you submit for A. So if your letter from A states, “Person has worked in the position of Manufacturing Engineer whose job duties are … such and such” that is absolutely fine. Logically if one takes every minor promotion in a company to produce separate verification documents, that will balloon to a mountain. I have been with the same company in multiple locations and various promotions and all I submitted was Location A… one designation. So that should not be a problem.
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For alternative employment verification methods, see Do not have reference letter from employer, Multiple NOC codes
Lastly I think the eligibility criteria notes the experience needed to qualify as the NOC code you used to qualify for express entry and the minimum criteria you have met already ( think its one year of continuous work experience?). As long as you have points in the pool, you should be good. But verify this thing with someone else too. What goes into the Express Entry point could be just the last experiennce from Company A and rest goes into “Personal History”. As long as you had points and the tool checked it for you, you are okay.
But double check.