I think it is quite common to be able to do so depending on what you mean by pathological.
For example a group might have been defined as 'atypical' or another named group at least due to not responding to a medication that the majority not only responds to but does so significantly and/or on an objective measure (eg skin clears up, increased function, increased wellness are complicated in where is objective vs judgment call/assessment?).
Is only going with those who have definable PEM going to mean that those who don't yet/aren't currently in that position (either because they can't discern it from the rest of their fatigue, or it's rolling PEM and they aren't going to be given a break soon etc or they don't get it as often, or even don't have it etc) aren't going to benefit from results/if there is a move forward?
Is PEM a better and safer 'proxy' from putting people through over-exertion for a long period of time vs deterioration (or retrospectively measuring for that) ?
If we wanted to take that analogy to 'treatment' and it were actually really a treatment then effectively GET, and any variations of it, or I think extrapolations of that paradigm/parody would be the same thing.
The difficulty or situation that we've had is due to that objective vs judgement call/assessment and who gets to do it and what their aim has been, or more precisely attitude to the null or alternative hypothesis has been (in allowing that to be 'made provable' if it is only true if the system sees it but the system won't see it) for ME/CFS.
PEM has sort of ended up in the middle of this assumed to be a/the(?) mediating factor by some when different types of exertion/over-exertion/insufficient recovery rest and the cumulative aspects contributing to both is perhaps the closest we are at currently.
Yet as a thought experiment has anyone who gets PEM ever benefitted from, or got more well despite, GET? we just don't know whether not triggering PEM (impossible for most) is either possible or avoids the deterioration of continual over-exertion ie 'riding limits' over a more extended period of time, and from my experience of riding PEM at least then the answer is no.
It is going to cause my brain to fuse out trying to think through the different groups and ifs and buts here (eg non-PEM but deterioration, PEM and deterioration and so on...)
and then it cycles round to this issue of the (deliberately in some circles) ambiguous definition of fatigue, not very rigorous descriptions of patterns of it and different types with different symptoms across all sorts of illnesses and dumping pots.
I mention these because one problem eg with PACE type things from the old days I remember rightly coming up was that if someone who had only depression was seen as having fatigue, and depression actually is a condition where people feel better and function increases with more 'doing'/exercise, then if someone filled a trial with subjects whom noone knew if they had one, the other or both you might actually just be re-testing 'does GET improve depression' rather than cfs or me/cfs and making claims based on extrapolation that is inaccurate, as well as in those with both not understanding how something can be both good for one and bad for the other (and then that eventually being bad for the first one too as people's health gets worse).
BUt as others have said there even in the cfs days was generally no actual benefit found so the claims of there being some magic, undefined group of people with cfs/me (in the term used by eg clinics who don't want to change away from GET and claims it's OK because they 'treat CFS/ME not ME/CFS') that can still be treated with something that is at best useless because maybe it doesn't harm them isn't something based on anything.