Formula for volatile date range

I have a range of daily data covering 01/01/2015 till today, and I need a formula that mirrors the length of days passed in 2016 so that I can sum the corresponding 2015 values.

So for example today = 21 Jan 2016, my fields to fill in are:
Sum everything between 01 Jan - 21 Jan 2016 - this one I can do it by sum everything >= 01/01/2016
Sum everything between 01 Jan - 21 Jan 2015 - this one is the one I am stuck with because I need the "21" to be volatile

Sample spreadsheet containing excerpt of pivot table and the partial report attached. Yellow cells are the ones that I am stuck on and I have filled them in with a manual sum to illustrate the desired sum range. Dummy reference cells are welcomed.

Any help would be greatly appreciated, thank you very much in advance!

Sample2.xlsx