The 'Total Distance Driven' at the top of the Driver's log is either the ECM recorded distance driven (if there was an ECM connection) or the GPS distance driven, but not a combination of the two.
This means that if there happens to be an issue with ECM connectivity in the vehicle the total accumulated distance may look incorrect.
Remember that the Driver log is a legal document displaying government required information rather than your business requirements (i.e. wanting to know the total distance driven regardless of the method of capturing it). So, if you want to see the combined total distance driven regardless of ECM connectivity the best way to do so is via the Shift Report.
Note: if you click the Driver's Name on the Driver's log it will take you directly there!