Need logic to get the base element from Retro run results elements

Summary

Hi Team, we have a requirement to get the project number and task number from base element:

Content

Hi Team,

we have a requirement to get the project number and task number from base element:
Example: 

1. Regular pay earnings retro results is the element which got processed in current pay period(Feb-10-2019 to Feb-16-2019) in run results.
2. for above element(Regular pay earnings retro results) source/base element will be "regular pay earnings results" which got processed in previous pay period(Feb-03-2019 to Feb-09-2019).
   now i have to get the "Project Number" and "Task Number" from base element, in My scenario we don't have "Project Number" and "Task Number" in "Regular pay earnings results" element so to get that we have to