Excel lookup data IF-statement

I got a problem where I have data inform of numbers with a certain date related to them.

My problem is that I want to summaries the monthly values that belong to the certain month. Someone before me is using : =IF(References!$M6,IF(HLOOKUP($C63,Elec_data, ROW(Q3),FALSE),HLOOKUP((DATE(YEAR($C63),MONTH($C63)+COLUMN(B1)-1,DAY($C63))),Elec_data,ROW(Q3),FALSE),""),"")

Where Elec_data is the saved name of that table to extract the data from. M6 is the month, C63 is also the month. I don't understand what COLUMN(B1)-1 has to be -1 also?

The function works but if there is no value in the column it still takes the next value in the column. It takes the wrong value to the cell for the month.

Thanks.