How to get the effective start date of existing assignment in Redwood validation?

Summary:

We have an existing validation rule in When and Why checking for the Start Pay Period and Next Pay Period but not working now in redwood since the HCM params CmpRespAdminSalary is not working. There is one working using the EMP_Groovy_ActionTypeCode HCM Params - CMP_CHANGE_SALARY - but this will trigger in other pages like in Salary History>Change Salary and we do not want that to happen. I am trying to rebuild the rule in Redwood but I could not find an effective start date attribute for assignment. Previously in autocomplete, I was able to get this value by going to