Errors in my calculations of course :)
As jonny63 pointed out, FIFA didn't include the two Cayman Islands matches vs. Antigua & Barbuda and Bermuda.
There's also a big difference for Cuba (also spotted by jonny63), but I'm afraid I can't find an explanation for that.
There's a problem with the matches played on September 3rd in previous years. Three of these matches affect the famous October 2007 top 20.
3 September 2004
Spain - Scotland 1 - 1
Netherlands - Liechtenstein 3 - 0
3 September 2005
Armenia - Netherlands 0 - 1
Moving them to different time frames, solved the differences for Spain, Netherlands and Scotland. However, I still have a 1 point difference for England and Greece. Hopefully, the guys at FIFA Information Services will be kind enough to solve this.
This is a very frustrating issue for me, as matches played on September 3rd are in different time frames for different teams.
Unfortunately, there are no fewer than 69 matches played on October 10th (when FIFA will publish the next ranking) in the previous four years and this will affect my calculation for October.