How do I get the balance for multiple TRUs in the same year?

Summary:

We have employees who transfer from one tax reporting unit (TRU) to another during the course of a year. We have an element for which we need the YTD (Year to Date) for some calculations. However when employees transfer to another TRU, the amounts are getting split by TRU and when we run, only the current TRU amount shows in the Fast Formula. How can I get the total YTD across TRUs?

Content (please ensure you mask any confidential information):

We're currently using ELEMENTNAME_REL_YTD, but we've also tried ELEMENTNAME_YTD. Is there a specific context we need to set to go through the history of assignments? We tried PROCESSED_PAYROLL_ASGS, but that didn't do anything either.