I have noticed that Rafael Nadal had more points in Race rankings than in world rankings in several recent editions of ATP rankings.
As far as I know, the race rankings are based on the tournaments from the current calendar year, whereas ATP world rankings are based on the tournaments from the last 52 weeks. So the latter includes longer period. How is it possible that a player has more points in the race rankings? Are there different rules for which tournaments are countable for these two rankings?
For example, as of August 19, 2013, Nadal had 9010 points in the race rankings and 8860 points in the world rankings. You can check this on Wikipedia (here and here or in the Race to London rankings and ATP rankings published on the ATP website.
When I check rankings breakdown on the ATP website then for the ATP Rankings I see (at this moment):
For Race to London I get the following:
So in this particular case, the difference seems to be that 150 points from the tournament in Viña del Mar in February 2013 are included in Race to London rankings, but not in ATP Rankings.
I do not know whether it is possible to somehow find ranking breakdowns from the past, but according to this blog post Vina del Mar was included on February 11th; but this was before the tournament in Sao Paolo. He had 5550 points on February 11th (after Vina del Mar) and 5755 points on February 18th (after Sao Paolo).
Maybe the rules about number of required ATP World Tour 500 series tournaments could explain this? According to Wikipedia: It is mandatory for leading players to enter at least four 500 events, including at least one after the US Open; if they play fewer than four, or fail to play in one after the US Open they get a "zero" score towards their world ranking for each one short.