If it's like the EC settlement the entire amount gets dumped into a 2017 1099 which means max tax. I hope to go over to the IRS office and see if my settlement can be applied over the 2001 through 2016 claim period in an effort to boost Social Security earning's years and while I believe the odds are slim to none I will try anyway.
You would need to file amended returns. If you do that, you may end up paying more in social security taxes. You need to amend and file as an employee with all your business expenses from schedule C being transferred to schedule A as unreimbursed business expenses. I looked into it, but going back over 12 years, you might have trouble getting the IRS to accept an amended return. There is a limit that they can choose to ignore, but not sure if the costs of the attorney or at least a CPA would be worth it. I think you can go back as far as 8 years, but unless they've itemized the payout by year, it won't be easy to figure out how much per year.