I'll try to explain better.
Since the geocacher in question isn't a Premium member (anymore), the geocacher can't see the coordinates of premium geocaches. It's impossible to calculate a distance without coordinates.
The checker had an issue where missing coordinates ended up being 0,0, which ends up being a quite long distance from wherever the geocacher usually geocaches.
When a premium member ran the geocacher all coordinates were visiable, and the end result was correct. When the none premium geocacher ran it, some coordinates were very far away, causing long distances.
The checker has been fixed and will now exclude distances to premium only geocaches. This is the only way it can be handled. Yes, buy not being a premium member you will get a lower result than otherwise. Since the geocacher is not allowed to view the coordinates of premium member only geocaches, the distance can't be calculated. This is all by design with the Premium membership and the license to use HQs data.
Both nil and false are invalid results. It doesn't really matter which is what for the geocachers. It should be considered a "missing coordinate". The checker developers however needs to do it right, but in this case it was our documentation that was wrong.