That does not sound like they were working in the main trunk. I do not believe you can run any production code that was self signed like this.
You can break glass in emergencies by committing code TBR, or "to be reviewed", however this automatically escalates to owners of the code in question plus your manager and director, and all TBRs have to be resolved by actual review within a short time. An author cannot submit to-be-approved code; they have to be owners of the code in question (personally or transitively included in the OWNERS file) to TBR.
You can read about this system here: https://cloud.google.com/security/binary-authorization-for-b...