Before the OPM data breach there was a hack of WikiLeaks itself. Pastebin had a dump of email addresses and password hashes associated with the accounts. I think it was in 2014, but am sure it was before the OPM data breach. Many government email addresses turned out to be registered on WikiLeaks, so various agencies had to take remediation steps for those email accounts. Anyone working at the time in federal IT space would probably know at least something about the incident.