11.5.7. The SessionFactory Registry SessionFactory Registry

While it is best practice to treat instances of all the registry types as targeting a given org.hibernate.SessionFactory, the instances of services in this group explicitly belong to a single org.hibernate.SessionFactory.
The difference is a matter of timing in when they need to be initiated. Generally they need access to the org.hibernate.SessionFactory to be initiated. This special registry is org.hibernate.service.spi.SessionFactoryServiceRegistry