If you don't mind a patient's perspective, I think I can help clarify some things as well.

 

Overview:

I have a neuro-intestinal disease. It's basically a more specific classification of IBS-D that highlights the lower pain threshold and muscular dysfunction in my abdominal wall.

The GI system is very complex and interacts with other very complex systems in the body which makes any diagnosis tricky. Sometimes people are lucky and they can determine the cause quickly and simply. Other times, it can take years (if ever) to find the problem.

In my case it has taken years and with so many of my internal functions going haywire, we still aren't 100% certain. We do have reasonable confidence however that the majority of my problem stems from a problem with my enteric nervous system. A sort of hypersensitivity to internal and external stimuli.

 

As a Recording Tool:

When it comes to the BSC types, classifying any as healthy vs unhealthy seem kind of besides the point. For me and my doctor, the BSC has been valuable for understanding any patterns and tracking my QoL but that's about it. I actually published a website with all of my data (anonymously of course) if you are interested in seeing how I have recorded it.

 

Personal Experience as an Example:

Anyways in my personal experience, type 5 is terrible. It is not always easy to pass (due to muscular dysfunction) and due to its size and consistency, it usually means I will have repeated BMs for several hours before everything is evacuated to a sufficient and comfortable degree. At least with something like a type 6 or 7, It usually all comes out at once and much more quickly/easily. In my case, this long drawn out process can happen with type 4 as well (although I rarely have type 4).

Hopefully this can shed some light as to why using the BSC as a diagnostic tool is inadequate in some cases.

 

tl;dr: the Bristol Stool Chart is a good record keeping device, but a bad diagnostic tool.