Vehicle history can sometimes become unattached from the customer record, this can be caused by a number of things.
To rebuild the vehicle history against a customer vehicle go into Customer > Vehicle > Update (next to the reg field) and Rebuild History.
The screen will pause for a couple of seconds while the system links all the historic history data back to the vehicle.
Close out the record and go back in to check the history.
*if this fails please contact the Navigator Helpdesk for further assistance.