Skill Mapping Data set in BI Reporting does not pull all mappings

Summary

Certain Mapping Data sets do not seem to provide all mapping data. When one creates a simple report to see all skill mappings, one expects to see Assignments mapped to the Skills. But they do not show

Content

When Learn BI provides a Data Set called "Skill Mappings", one would expect that all the mapped Items to a Skill will show up in this data set. I have Assignments mapped to Skills. Just simply, one Assignment to one Skill. I created a custom BI report and used the Skill Progress Data set. It has Skill ID, Mapped Item ID , Mapped Item Name etc. I expected to see my mapped Assignments to the Skills in that list. Assignments don't show up. Other mapped Items to the Skill are displayed. But not assignments.