Customer Exit Code

Dear Sap BW Experts,

What is wrong with below piece of Customer Exit Code. Bex Query is not fetching last year data.

CASE i_vnam.            "Sambhaji for last year 12 periods

   WHEN 'ZPYR_PRD'.

     IF i_step = 2.

       DATA l_yr(4) type N.

        CLEAR: l_s_range,loc_var_range.

        LOOP AT  i_t_var_range    INTO  loc_var_range   WHERE  vnam = '0P_CALM2'.

          l_yr = loc_var_range-low+0(4) - 1.

          CONCATENATE '01'  l_yr INTO loc_var_range-low.

          CONCATENATE '12'  l_yr INTO loc_var_range-high.

          l_s_range-sign   = 'I'.

          l_s_range-opt    = 'BT'.

           APPEND l_s_range   TO   e_t_range.

           EXIT.

        ENDLOOP.

     ENDIF.

  ENDCASE.