Count unique values on a specific date

Hello, again I need help from you guys. This time I want to count active customers at December 31st every year (2008-2013). Most customers are listed twice on specific dates, but I want to count each customer only once on the specific date (31.12.13). One thing that complicates it a lot is that some customers has term period some other date than 31st each year so that I cannot use 31st as a sorting element. Customer 2 has for example a term period 14. march each year, but it is still active 31st each year. Customer 3 has term period in february. This customer was active in february 2013, but inactive december 2013. I will therefor not count customer 3 as of 31st of December 2013.
I have attached a sample data.

Anyone?

hi,
does the attached file do what you want ?
rgds,
AL
customers_AL.xlsx

I figured out a way to count the unique customers. But the problem I am now facing is to count the relevant customers. I need to count only the active customers on 31st of each year. Since they all have different periods it makes it difficult. For example: Customer 2 is active on
22.February 2013 and since it doesīt have an inactive date it is thus active on 31st of December 2013. Customer 3, however, is active 22nd of
February 2013, but inactive 1st of December 2013, so therefor I canīt count customer 3 in 2013. I have attached a new file.

Hopefully somebody understands my challenge.

Thanks - that is an awesome formula. It looks like it works perfectly. I need to check it out on my entire data range (appr. 9000 rows) when I get to work on Monday.