FRS Report Accounting Period : Range & Match

Our FRS (FRWS) Report Income Statement Report has two Grids in it. Grid1 runs for the Accounting Period. Grid2 needs to always has to return the ending balances for DEC period of previous year that Grid1 is using. The ending balance from Grid2 (Last year DEC period) will be deducted from Grid1 ending balance. Therefore we are using the function Range (with offset from -12 to -1) AND Match on DEC in Grid2 Accounting Period. When the report is run for SEP-23, (we expect Grid2 to fetch DEC-22 ending balance), Grid2 returns the value DEC-23. I suspect this is