evidence: The most sensitive classified documents are serialized, for example, whereas less-sensitive files are not. There are some documents so sensitive they cannot leave the room in which they are presented. But it is important to note that the majority of classified government documents are not tracked item by item. [...] The most highly sensitive classified documents fall under a check-out system [...] The process for regulating the whereabouts of classified documents is challenging because some such information can live on through administrations, Cohen said. It is also possible that the president, vice president, or an administration staffer removes a few pages of a larger classified binder.