Count orders after date x ONLY from customers that also ordered 3-8 weeks before date x

Hi guys,

I started a thread on this topic a while back, but have not been able to complete my analysis by a fraction. In case starting a new thread on the same topic is against ExcelForum etiquette, I apologize. I simply hoped this would bring the issue under new attention.

My workfile consists of two tabs. The first is a sales sheet holding over 19.000 ordered products, divided over more than 10.000 orders by over 5.000 customers. The second tab holds a list of 778 customers by e-mail address, all part of the database in the first tab, as well as 778 non-unique dates. [SAMPLE FILE: Sales database SAMPLE.xlsb]

What I am looking for is a method to calculate column Summary!J. This column should show the number of orders since the dates in Summary!F, but ONLY from those customers that had also placed an order in the 3 to 8 week period running up to those dates. Cell Summary!J3 holds a working formula, but is quite inefficient. Every time I try to copy it to all cells in the column, Excel freezes.

Therefore, I was hoping someone could help me out with a method less straining on my laptop's RAM. Elegance or ease of use doesn't matter to me.

Thank you in advance and kind regards,

Stijn

On the OzGrid forum, I was just notified of the cross-post policy, so hereby the link to my similar post there: http://www.ozgrid.com/forum/showthread.php?t=173511. I apologize for not doing this right away.