Like Nicole said, Rihanna songs usually blow up once the tracking period for IFPI begins.
Besides, Rihanna has like a single out every month so she should have more than one entry.
You can't deny the facts
The fact that she releases a single frequently helps her overall digital sales but it hurts her individual single sales so negating a whole month and a half of sales for her lead singles (typically her biggest WW singles) would obviously hurt her, not help her. Anywho this was fun!