"I never sold my stock. Fidelity sold stock on my behalf for paying taxes on it."
ALL of the stock was legally yours the minute they vested. If you had reached into your own pocket and said "here's the cash for the taxes" then you'd still own all the stock. You consented - maybe without understanding - to selling enough stock "for taxes". Fidelity may have executed the trade but YOU sold the stock.
"I havent sold any of the stock that I actually own post taxes. In that case, should I be using the Adjusted/Corrected Cost Basis?"
It's entirely irrelevant if you sold some of the stock - for taxes or otherwise - or none of the stock. The point you need to understand here is the taxes needed to be paid at the vesting because you recognized COMPENSATION. Those taxes have absolutely nothing to do - nada, zip - with a subsequent sale of the stock. That's a COMPLETELY SEPARATE EVENT! The only connection the sale of the stock has to the compensation event is that the per share basis is the SAME AS THE PER SHARE FMV USED BY THE EMPLOYER TO CALCULATE THE COMPENSATION. You need to understand that.
I can't see whatever the broker is telling you on the supplemental information but if they are using a per share dollar figure for the cost basis that's the same as the figure used to calculate the compensation, then yes, that's what you use.
