I think that manicures, polish, etc, can distort the window here.
Also, there seem to be be many interpretations to various nail signals.
For instance, fewer than 8 lunulae has "many" rule outs. and then about injury; "If you know you have traumatized a nail and it is black, blue or various shades of bruise, this is not really anything to be concerned about"; another illustration is that different issues can have the same root cause. This could be used to understand that if you have 2 or more "signs" pointing to one or more issues, the combination of the signs can be used to narrow the problem focus.
I believe the right hand\left hand illustration here... my left ring finger lunulae was the last to appear early this year. When I started all this over three years ago, I had lunulae on my thumbs and barely perceptible on my right index finger. Lunulae always appeared on my right hand first... I am right handed. In addition, as I began to use my left hand more and more efficiently for tasks I normally only used my right hand for, the lunulae became more pronounced on the left hand.
Nail health and "signs" can be used as a useful diagnostic.
However, if people receive or give themselves manicures, along with the polishes, nail removers, moisturizers, and such, this method of determining health is most likely out the window, at best, distorted, and one must use skin, hair, digestive, elimination, and oral health signals\signs.
As illustrated in the last sentence above, I think that we have been given many "backup" systems to use as signs\signals to determine our overall health AND well being.