"I am assuming I will have to go through the trade reports from when the RSU stock portion was vested and take the fair market value from there as my MetLife basis, is that correct?"
If you are or were an employee of MetLife and received shares due to the vesting of an RSU then the per share fair market value of the stock on the vesting date is your per share fair market value. The trade reports, W-2's or other contemporaneous information is the best source for your "original basis" before the spin off or any thing else that may have affected MetLife basis along the way.
It sounds like the broker, or somebody, did some sort of a lot-by-lot calculation here for some reason and I have no idea why.
But the CIL transaction really is a single sale and there's no need to do any income tax return reporting that's more granular than that. Report the proceeds, report a basis, and you're done.
If you're meticulously obsessive - I lean that way - then you could go through the exercise of determining how much the basis of each lot is, add up the individual lot figures, take 10.3635% of that total for your basis number to use to report the CIL $47.48 "sale", then spread that amount back to each lot as a small reduction in each lot's basis, based on how much lot's basis, as a percent, contributed to the total basis.
On the other hand nobody but you is going to know if you say "the hell with it" and simply report the CIL with no basis, which I expect happens in 87.35% of all CIL's reported on all 1099-B's during a year.
