According to the webmaster, there may of course be errors to your information given and they refer to this as “human error.” I quote:
Furthermore, there is a possibility that your name, date of birth, or other personal information as you know it, may have been incorrectly encoded inadvertently. This is called human error… and it happens. If this is the case, the PRECINCT FINDER will most likely give you a negative result, or a result that you may not agree with. You may try to be “creative” with how you input your registration details in our Form, by following some tips that we have provided here.
Because of this, they have a backup plan. Check out the precinct finder tips and tricks for such cases when your name may contain suffixes like “Jr.” or “Sr.” In fairness to them, I was able to find my voter information with only one try given that my complete name is more than 4 words long.