Sum values in cells based off of project name and project end date

Greetings all!

I have a spreadsheet that I need to be able to check if hours are allocated for labor per project beyond each project end date.

The format of the spreadsheet is as follows:

Row 2 contains "Description Headers" Employee, Project Name, Start date, End date, Dates by Week (ie... 01/07/13, 01/14,13, 01/21/13...) through the end of 2015.

Project Name: Column L
End Date: Column N
Dates by Week: Column O through DM

This is going to be a part of a larger error check that will be found on a seperate worksheet. I have attached a sample of the data.

Many thanks in advance for your help!