I don't know how they came out with herrmanii being a nat hybrid of helenae and hirsutissimum.... The pouch, plant habit and general appearance makes it possibly an hybrid of henryanum ( which of helenae or hirsutissmum has a pink pouch? None).
Maybe Averyanov has seen a natural hybrid of helenae and hirsutissimum, then it is not described. But in his early days, he trusted a lot some traders that were very dishonest, and gave him a lot of false information ( like barbigerum from Lam Dong, or the dendrobium suzukii from Son La
).
Herrmanii has been bought the first time on a street market in Hanoi, as a single plant, by accident. Then a few years later, a complete colony came out of the jungle (like trantuanii), thousands of plants. Then, it disappeared from the trade. However, if nearly all the collected plants of 'trantuanii' ( no matter what they are really) have disappeared, some traders in Dalat still have big, well grown, clumps of herrmanii.
herrmanii comes from about 100km west of Cao Bang, quite close to henryanum. The only colonies known have been collected a long time ago, in massive quantities. Sometimes the collectors bring a few plants, but it is indeed rare. selfings of herrmanii by Klinge gave only herrmanii, no variation, the plant size shows considerable variation, like henryanum.
So far all the plants that were sold as natural hybrids in Vietnam of esquirolei turned out to be very large coccineum, or henryanum, or plain esquirolei. Natural hybrids of esquirolei are exceedingly rare.
A natural hybrid is the progeny of A x B
A natural hybrid swamp, like herrmanii, is AxB, the crosses back to A or B, between them, etc... After some generations, it becomes very constant, and slowly will undergo differentiation as a new 'species' or 'variety'.