WTPart history authorization column information.

Its complicated as you can tell from that article. Knowing process is key to narrowing the focus on how Parts are released. If they are only from Change Notices, you can expect to find one linked to any released version. If they are from Promotion Notices (Requests), then you need to look for those. It could be both, or you can have some one that manually came along and set the state in which case it would be a person. Which API depends upon which object did the release. I would setup a series of if/thens to capture each case or eliminate ones that the process does not support.  There should be helper APIs for getting resulting items from Change Notices or from Promotion Notices. Let me know if you need more assistance.

This is the data utility that generates the data which could help you.