There is currently no strongly linked method to track the conversion of defects, stories, or epics. If I have a defect that was converted into a story, then an epic, or maybe back to another defect there is no clean way to do this and know the relation between one defect, story, and another defect. It seems to lack any type of "converted from" or "source asset" attribute, at least from the metadata API side which causes limitations in potential integrations. Soft links would be nice so recursive API calls are not needed, while removing the potential false positives for matching relationships.