In the realm of logic used in the real world, information is assessed by it's probable reliability in the eyes of the investigator (or judge or jury), some things may stand on their own or require only a single source because they are obvious. Some things may need more than two sources before they are even taken into consideration. As I said above, it depends on the reliability of the information in the eyes of the investigator.
While that is also true, it is nevertheless the exception, not the norm, to have a single source that is reliable beyond any reasonable doubt. Usually at least two independent sources are needed, and we are back at the premise I quoted.
In the case of MH370, neither Inmarsat nor the Malaysian authorities qualify for that level of credibility and integrity.
The Inmarsat data on its own is as close to scientific fact as anything can be, the data and methods have been evaluated by known experts in the various specialty fields and there has been zero disagreement among the experts that the Inmarsat data is valid and the Inmarsat interpretation of the data is also correct.
Please reconsider this statement. As I said this is a fallacy. While the methods to analyze the given data and the subsequent results might be considered valid, that says nothing about the integrity of the source of the data itself.
Also it is incorrect that experts say the source data is valid qua apodictum. I read several analysis where the "experts" state scientifically correct, that their analysis is based on the ASSUMPTION, that the source data is valid.
The radar data provided by the Malaysian government in their Interim Report is also reviewed and crosschecked, this time not by scientific peers but by investigators, journalists and the general public. Malaysia has stated that their military radar saw MH-370 turn around at IGARI and this fact has been corroborated by both the Vietnamese who have stated that they saw the same turnaround on their military's (primary) radar and a Thai sighting of what can only be the same target a few minutes later approaching Koto Bharu.
I'm not aware of a confirmed Vietnamese source seeing a turnaround on primary radar.
Neither did the Malaysians ever claim to have tracked a turnaround. Secondary was lost 1721UTC during a straight NE heading, and primary first picked up an UFO - at a straight SW heading - at 1730 UTC.
http://mh370.mot.gov.my/download/FactualInformation.pdf
So let's say the turnaround is an ASSUMPTION. Under the ASSUMPTION that that object on primary is 9MMRO, the turnaround is then conjured. Or do you have other sources that I'm not aware of, neither are the Malaysian authorities?
...So we are left with a report which we can accept with a very high level of confidence fitting perfectly with another report that has been so thoroughly analyzed by experts that is stands for all practical purposes as scientific fact.
Again, a formal fallacy… Where do you take that "very high confidence" from? No matter how scientifically correct and elaborate you analyze data, if you can't verify the source of the data, then you can ASSUME all kind of scenarios, chains of events etc., but it is not factual in its results, even if it is scientific in its methods, best case. It's a hypothesis, based on a premise of certain assumptions, not fact.
A prudent person would now accept this as fact and move on from here.
A prudent person would look at the elaborate building of speculation - or hypothesis, since that sounds more positive for the more educated speculations about 9MMRO's fate - and see it as what it is. It might eventually be proven to be true or close to truth, or it might turn out to be false, or we will never know, but please let's separate fact from fiction.