YTD Sum of Multiple Years

Hello out there,

New to this site so excuse any lack of knowledge of accepted posting standards. I'm having trouble doing a year to date sum. Referencing the attached workbook, I want to be able to write a formula that can look at a month of the year, use it as a base, and sum up everything above that cell within a range. I would like to do this without using individual month dates if at all possible. Thank you.