I had typical PEM before, both physically and cognitively induced. Cumin (cuminum cyminum) blocked my physically-induced PEM 100%, and after 2.5 years of treatment, I no longer triggered on physical exertion. I sometimes trigger on cognitive exertion, but sometimes not. so, does that mean I only have ME part of the time? The baseline symptoms continue even without PEM, so the disease is still there. The fact that I was able to block PEM with a chemical (cuminaldehyde) implies that other people might be able to block that pathway(or another) with endogenous chemicals or something in their usual diet. Another possibility is genetic, epigenetic, or other individual variation that doesn't support the PEM mechanism. If someone matches other PWME's symptoms and responses very closely but don't have standard PEM, I'd accept that as ME. I wouldn't select them for a standard ME research study though. They might be great for a "what's different about this person" study.
The CCC--and all the other criteria systems--fit some percentage of PWME, but there will be some percentage of outliers that just don't fit but still fit in many other ways. It's not an absolutely accurate system; it's just better for most purposes than Fukuda or other systems. Studies are hard to compare if they used different criteria. I just checked the ICC as well, and I'm not sure which is better. I still think I fit some of the categories as "sorta, kinda, sometimes" rather than clearly and positively.