TurboTax does not import the composite tax document that the broker sends you. That document is a human-readable PDF or printed document that the TurboTax software cannot use. The brokerage creates a special computer-readable file of data specifically for importing by TurboTax. TurboTax can only import what's in the special import file that the brokerage provides.
Errors do occur in importing data. There are two companies involved, and lots of moving parts, so there's plenty of opportunity for slip-ups. You can't rely on just checking that something was imported. You have to check all the details.
