by JP Slavinsky.
Actually, I just found the answer in the LTI 1.1 implementation guide. Go figurelis_result_sourcedid=83873872987329873264783687634
This field contains an identifier that indicates the LIS Result Identifier (if any) associated with this launch. This field identifies a unique row and column within the TC gradebook. This field is unique for every combination of resource_link_id / user_id. This value may change for a particular resource_link_id / user_id from one launch to the next. The TP should only retain the most recent value for this field for a particular resource_link_id / user_id. This field is optional.