Hi @k457,
Starting with version 3.2.0, PKP applications (including OJS) support the concept of versioning, whereby multiple versions of a submission can be created with metadata changes preserved. A submission (article) might have several revisions. These are called publications. So it’s not safe to rely on submission IDs being the same as publication IDs, and a single submission may have several publications (if it has been revised).
Regards,
Alec Smecher
Public Knowledge Project Team