Discrepancy between History Override & Adjusted History

Hi All

We are running demantra demand management for our forecasting need. We are making manual entry over base history ( Booking - Book items - Req Date) to get an adjusted history. In most of the cases, history override value is matching with adjusted history value.

However, in some cases, we can see that adjusted history is not same as history override! This is happening irrespective of items or other level criteria.

Is there a formula which calculates adjusted history from base history & history override? What other factors contribute to adjusted history not equal to history override value always?

Thanks