Count if the sum of columns meet a condition

Hi all,

I need your help. I want to set up a formula (countif???) to count the number of customers for each year in row 12 (file attached).

Some customers don't buy anything for a year and then come back, which should be included in the count for that year. For example, customer C, F and H should be included in the count for the years 2012, 2007, and 2012 & 2013 respectively.

I'm thinking to include customer C in the count of 2012 if sum(K4:L4) >0, but I don't know how to set up the countif formula to do that.

I know I could create a dummy worksheet and run a formula for each cell to place 1 on each cell if the sum of the subsequent cells in the row >0, and then sum all the cells (i.e. 1s) in each year/each column to have the number of customers. If there are so many customers, my file might get big with the dummy worksheet.

So it'd be great to set up a formula in row 12, instead of the dummy worksheet.

Please help.

Thank you so much!