That is correct, it is the collection of experiments and correlation analysis, and that does not establish "direct causal link," but rather likely common cause.
I agree. There is a weak correlation. In some cases that correlation is also correlated in time. This is why I think it such a waste to pursue such inconclusive speculation. Even if there existed some deuterium reaction which created helium, it is unlikely to be significant in light hydrogen systems. And in the event you believe in some form of fusion, then surely the proton, with its reduced mass is going to dominate ALL possible fusion reactions! If 23.8 MeV is expected, it is expected only by non scientists!
This is bizarre. Heat/helium is only asserted and found in deuterium experiments, not hydrogen. The statement about non-scientists is simply crazy and belied by what actual scientists have written about this.
Helium was not expected in 1989, the largest reason being that the gammas believed to be necessary (from d+d -> 4He, the rare branch) were missing. Pons and Fleischmann had found some helium in the outgas and that was announced early on. Then they shut up about helium and actually tried to stop the publication of the Morrey collaboration results. Essentially, those results contradicted their idea of what was happening and they were spooked. It was a very bad decision. They had apparently measured helium in experimental rods, early on, those results were promised, but never released. That is what led Park to be such a skeptic! At least that is what he claimed.
A few theoreticians suggested the helium might be possible. My sense of early cold fusion theory was that it was a collection of valiant attempts to come up with some explanation other than "error."
It was not until Miles announced the correlation in 2001 or 2002 that serious evidence existed. Yes, 23.8 MeV/4He heat would not be expected from d+d-4He. Rather from that branch, besides being so rare, a 23.8 MeV gamma would be expected.
But this is what accumulated as evidence: No ash identified and correlated with heat except helium. No major radiation. If we assume the fuel is deuterium, which is certainly plausible! -- and they did do hydrogen controls and saw little or no heat -- then 23.8 MeV/4He does become the expectation from the laws of thermodynamics, which are mechanism-independent.
This is all well-known in the field, accepted by almost all the researchers -- very few exceptions -- and ... is now the subject of a careful effort to measure with increased precision.
Heat/helium is only found in heavy hydrogen systems. The very existence of light hydrogen results is not well established. The ash is not known. (Storms thinks it is deuterium, which requires a more complex reaction, ie.., p + e + p -> d. Or something like that. Storms then proposes a mechanism which supposedly works for protium and deuterium.)
But this is my basic point about cold fusion. Theory is not terribly useful, yet. The actual reaction is a mystery. What is needed is more data, to feed theory formation. And that is going to take money.