Quickly from testyoursystem.000space.com

With no rules:
There were 10400 races for the System
There were 10418 Winners for the System for a strike rate of 10.4%

With 1 to 21 days

There were 10274 races for the System
There were 6892 Winners for the System for a strike rate of 10.78%

So its probably not that stat as it only makes it 66%.