RECENT is apparently storing WorkObject key but absolutely no information regarding associated assignments. And that make sense because having a recording a previously executed assignment will not be helpful (assignment is gone already)
Customizing will be possible of course but I guess it will be a significant amount of work and testing of course.
I read your document and what is understood, you are using pyRecordKey which contains pzInsKey of work object. If you want to open it in perform mode, you need to pass assignment key. Using pzInsKey, try to get Assign-Worklist instance pzinskey and supply that to open assigment action set. That will definitely work. Hard part is you need to get Assign- instance pzInskey by using case pzInskey.
Your work table and Assign table link is .pzInskey=.pxRefObjectKey.