I know basis information has to be supplied to taxpayers now, but I believe it is only after a certain date, and if accounts were transferred to another brokerage then #2 is not responsible for basis prior to any purchases made through Broker #2. Also, does the IRS really match these basis figures as reported? I believe there is a way to use what is reported, and then use the adjustment column on Form 8949 to reconcile to your figures , is it not? I wouldn't lose a whole lot of sleep over it. I think you have done due diligence. I would not hold my breath waiting for Broker #2 to adjust their numbers and issue a new 1099.