Question:

Why are related records missing from an object record's exported audit trail in Vault?

Answer:

When exporting an object records audit trail, a user has the option to 'include related records' in the export.  For example, when exporting a checklist's audit trail a user can also include the audit trails from the checklist's related response records.  However, Vault limits the export of related record audit trails to the first 100 related records that were created.  Vault also enforces this limit when selecting the 'Get History' option from the primary record, which displays the audit trail of the primary object as well as the first 100 related records.  If the primary record has more than 100 related records, the additional related record audit trails will not be included on the audit trail export of the primary record.  

Related Documentation:

Vault Help Documentation: Related Record Audit Trails