"What's still confusing me is that my 1099 form reports on only the shares sold for tax purposes."
Since a 1099-B reports security SALES and if you only SOLD 8 shares, then your 1099-B is reporting the sale accurately. Understand the the compensation income created by the vesting has absolutely NOTHING to do with selling any shares. If you'd reached in you pocket and handed your employer ~$80 to pay for the taxes your W-2 would look EXACTLY the same as it does now, and you'd own 20 shares instead of 12.
"Are you saying that when I enter this transaction in TT, I enter $80 for proceeds, $80 for cost basis (or exactly as the form states), and then on adjusted cost basis I put in $200 for the gross amount?"
No, absolutely not. Your per share basis is whatever your employer used to calculate the vesting on the 20 shares and, as I said "The correct basis is: (# of shares sold) x (per share basis for that lot.)".
I doubt that the broker is actually "reporting" the basis in the sense that it's being reported to the IRS. Sometimes brokers do put your "real" basis on the paper 1099-B you're reading but also tell you that the basis is not being reported to the IRS meaning that the IRS will see "$0" in that field.
But here's the real deal: as long as you report the trade accurately from a gain/loss perspective you don't have to worry a whole lot about how you get there. Report ~$80 as being on the 1099-B, even if it's not, or report $0 as being on the 1099-B and then adjusting to that ~$80; either way you end up with the exact same gain or loss and that's all that actually matters, not the "mechanics" of the actual reporting.
