Since you have already updated all of your work experience, you should upload reference letters for all.
To dig deeper, you have to upload reference letters for the number of years you have claimed under FSW to score 67. That's mandatory. Else, your profile will be rejected on the grounds of "FSW not met".
FSW is clearly mentioned under :
https://www.canada.ca/en/immigration-refugees-citizenship/services/immigrate-canada/express-entry/eligibility/federal-skilled-workers.html
Once you clear FSW, then for CRS, one gets maximum points for 3 years of work experience. To clear this stage, you will have to share reference letter for 2015-2018 and 2018 - Till date. But if in FSW, you have claimed more than 3 years of work experience points, then you need to provide more reference letters.
Which also answers your question about primary NOC, if you are going before 2018, what's the harm in keeping NOC 1112 as your primary NOC???