In column A I have Month, Jan, Feb, €¦.Dec.
In column B I have Heading Year 2003 with data for each month.
In column C I have Year 2004, with data
In column D I have Year 2005, with data until April
In column E I would like Sum for Last 12 months.
So cell E2 would be Sum(C3:C13)+Sum(D2)
Cell E3 would be Sum(C4:C13)+Sum(D2:D3)
But this needs adjustment if I wish to pull in down the full column E.

Is there a formula I can pull down which allows me to sum only the last 12
months for which I have data?