The scientific process is about the cumulative evidence. The scientists have in general trust that the others do not cheat, but they do not trust that the others are right. Being skeptical of every result that has not been verified thoroughly by several independent studies (unless the result is easy to prove) is a basic feature of the scientific process. This general skepticism makes any specific type of proof to have less significance. Therefore the principles are most important, detailed rules help by making the process more efficient, but they are not as essential.
A corollary of my previous comment is that very much of the knowledge used from climate science is not yet at the level of well established scientific knowledge. Even for results, which have not been contested, the evidence is often too thin. This is not a problem for science itself as it is really an unavoidable part of science. It is, however, a big problem for the use of the results of climate science in decision making. The climate science has produced very much preliminary knowledge waiting for better confirmation. This preliminary knowledge is not worthless and is often rather strong, but using it is problematic, as its reliability is difficult to estimate. This is a situation of PNS. Science proceeds in parallel, not undisturbed, but proceeds anyway.
For the NAS the same PNS type problem appears in many fields of research. All research related to health issues is very severely influenced by these problems. When the results of research are used in decision making the need of formal rules becomes important. Then the conflicts of interest must be taken seriously and steps taken to reduce their improper influences. In climate issues the direct conflicts of interest are less common, but political ideologies have taken to some extent their role. There are, however, no comparable possibilities of declaring political views of scientists.