Quoting from rabies wiki.
The period between infection and the first flu-like symptoms is typically 2 to 12 weeks, but incubation periods as short as four days and longer than six years have been documented, depending on the location and severity of the inoculating wound and the amount of virus introduced.
Six f*cking years? How is that supposed to be?
That 6 years could be an outlier. That 6 years is based off someone's health report. There are many variables that could affect said report. Such as an error by the doctors (doesn't matter whether human or machine). Since humans aren't alike, they body's immune system may have been weaker because of a pre-exisiting condition and so on and so on.
You get the general idea, the 6 years isn't solid.