It is possible that 2010 has turned on a default to remove job logs older than a specified time - looks like the default is 30 days.
Look in BE console:
Tools --> Options --> (Settings) Database Maintenenace --> Delete Aged Data section
If it has done this then the job logs are just XML files in the Data folder - so you will need to change the setting and then restore the XML files (assuming that the Job History is being kept for longer as the Job History provides the Database (console history view) links between the job and the job logs)
BTW - you have posted a BE question in a BESR forum.