If it's an organizational process, procedure, policy it's an OPA. It's usually not updated by project but influences the project. Eg: Change control procedures, HR policies
Artifacts created by project are OPAs. Eg: Lessons learned etc
Templates developed or tailored by organization are OPAs.
Anything outside process, procedure, policy, but pertaining to your organization are EEFs. Eg: Org structure, Hardware, software systems, Resources
Influence from outside the org are EEFs. eg: political influences
Industry standard templates are EEFs.
If it's a "system" it's EEF, if it's a repository (data) it's OPA. Eg: Configuration management knowledge is OPA, Configuration management system is EEF.