Consider that a fire in one building in 1973 destroyed millions of military records of which there were no copies, ruining bookkeeping for military personnel who had been discharged up to the 1960s.

The world was much less digitized even in the 1980s. A lot of records were still kept on paper or microfiche.

In the world of The Terminator Skynet’s first move was to nuke population centers. That means destroying untold numbers of records. Sure some military and high level government records would be on ARPANET but not nearly what we are used to today would be digital. Anything physically filed was basically gone though. Thats a lot of blank spaces.