While it is unclear whether her inability to remember stemmed from a concussion she suffered in 2012, it is interesting to look at some of what she could not recall.
Hillary Clinton's inability to recall things
Forgotten facts about security and classified documents
Hillary Clinton told the FBI that she could not recall when she received security clearance.
She further stated that she could not remember if she received training from the US State Department regarding the handling of classified information, the handling of top secret "Special Access Program" material and retention of federal records.
She could neither recall using her authority to designate material as classified.
Forgotten facts about emails
Clinton told the FBI that she could not recall getting State Department guidance on email policy.
Neither could she recall receiving emails which she thought did not belong on an unclassified email server.
She could not remember which aides had access to her email accounts and her Blackberry.
Interestingly, she also couldn't recall the process for deleting emails.
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Other forgotten facts
Among other things, Clinton could not recall the process one had to go through to nominate targets for drone strikes.
She could not remember a single briefing after she suffered a concussion in December 2012.
Neither could she remember any Freedom of Information Act requests sent to her regarding her emails, although she was notified of a FOIA request on 11th December 2012.
The implications of Hillary's inability to recall things
Hillary Clinton signed a Non Disclosure Agreement on 22nd January 2012 which read "I hereby acknowledge that I have received a security indoctrination concerning the nature and protection of classified information."
Therefore, her inability to recall her training has implications.
Either she committed perjury by signing the NDA without receiving training, or she lied to the FBI.