I have a theory that I am testing and if you have any experience to share that would be wonderful.  If content with Certificate assigned via API, the API assign content does NOT look back to reset previous completion and it disregards the rules of the Certificate.  If you want the completion to be reset then you will need to include that in an API call.  Additionally, if you want a new updated cert to follow completion then that too is an additional API call.  The summary here is that I believe if started with API grant access then it is additional API calls to manage recert and progress reset. 

The LMS/LXP is assuming you have a complete API workflow.  The LMS does not handle API grant the same way it handles Admin grant access or Learner elective grant access.  Your input will be so appreciated.  Thank you.