June 20th, 2008
Problem solved: link.
Take a look at USA results in 2007 (you need to press the "Prev." button a few times). The first match of the year was a 3 - 1 friendly win against Denmark in Carson City on January 20th, 2007. It was the first competitive match for the USA after losing 2 - 1 at the hands of Ghana at the 2006 World Cup on June 22nd, 2006 in Nuremberg.
After the Denmark match, there was another friendly win (2 - 0) against Mexico in Glendale, 18 days later - February 7th, 2007.
Now, please take a look at the detailed point totals published by FIFA in October 2007 -> pdf file. Scroll to page 18 (to check the USA point totals). Between Ghana - USA 2 - 1 (played on June 22nd, 2006) and USA - Mexico 2 - 0 (played on February 7th, 2007) there is no other match.
It doesn't make much difference for the October rankings: 886.24 instead of 885.94. The rounded value is still 886.
According to an e-mail from FIFA, the USA - Denmark match became an official match in the spring of 2008, after a request from the US Soccer Federation.
Still, with this match included, my total for April 2008 for USA becomes 890, FIFA has 889. The same 1 point difference for USA appears for May 2008, then all hell broke loose when I compared the June 2008 totals. With the exception of Argentina, my totals are way different from the ones published by FIFA. I can't quite figure out why... Did they recalculate the point totals for the rankings starting from February 2007 and then used them for the June 2008 ranking?
According to this article (Argentina consolidate their lead), a total of 347 international 'A' matches have been taken into account in compiling the world ranking for this year. However, according to the "Fixtures and results" section of FIFA.com, only 337 'A' matches have been played in 2008 (up to the beginning of June). Or does this figure (347) include the 10 matches played after December 17th, 2007 when the last FIFA Rankings for 2007 were published? More to the point, according to the FIFA Ranking schedule article, the deadline for matches is the Thursday prior to the release date. With the June 2008 rankings published on June 4th, the deadline for matches should have been May 29th, thus 28 matches played on 30 and 31 May wouldn't have been included in the calculations.