The achievement is unlocked when you obtain 80% of the archives. You can check your progress by pressing the menu button
, tabbing to Intel, and checking under archives. The earliest you can unlock the achievement is during the third playthrough because 80% of the archives are not available until then. Archives can be found in chests, revealed during story progression or by doing side quests, or (as is the case with the Pearl Harbor records) by checking a terminal.
The achievement can be bought at the special achievement shop that becomes available after the third playthrough. It costs 50,000G.
Track your progress as you approach the 80% mark. Make frequent saves. If the achievement does not unlock when you reach the 80% mark for archives found, you have probably experienced a glitch. In the event of a glitch, clear the cache. To do so, turn off the console by holding the
button on the console for at least ten seconds and then unplug the console for at least 20 seconds. Load the save you made just before reaching the 80% mark. Clearing the cache will most likely remedy the problem and the achievement should unlock when you reach the 80% mark of archives found.