A record is authentic when its origin can be traced and confirmed and it is what it claims to be: created by who it says, when it says, and not substituted or forged.
Authenticity is protected by controlled systems, version history, and clear naming, and it is undermined by forwarded or edited email threads that obscure the original. The test is whether you can show who created the record, when, and that it has not been substituted.
Authenticity is about origin: proving a record is genuinely what and whose it claims to be. Integrity is about whether the record has stayed intact and unaltered since. A record needs both to be trustworthy evidence.
IAR turns terms like this into working practice: assets classified against your disposal authority, stewarded by position, and ready to evidence.