A reply to both Brad and Richie.
The one last definite piece of evidence is the 157/337 radio message. Unfortunately there is no indication of where on the flight path Earhart and Noonan decided to adopt that course in search for Howland Island. So if they had overflown Howland Island then they were flying that line over a rather big stretch of ocean. If they had headed NW then chances of finding land are minimal, if they flew SE bearing in mind the sun position above the horizon and the difficulty of distinguishing cloud shadows from islands then finding land is still difficult even though there are better chances on the south-eastern leg. The same applies if they adopted the 157/337 line if they were short of Howland Island on their chosen course. So even accepting that they flew the 157/377 line does not provide us with a certainty that they will sight Gardner on that course.
So what happens then leaves us with four believable scenarios as distinct from the abducted by aliens, spying for FDR or similar flights of fancy. These are -
1. They overflew Howland Island and ran out of fuel and ditched in the ocean. After an unknown time they succumbed to sharks or just drowned. The remaining physical evidence of that would be aircraft wreckage somewhere in a vast area of ocean.
2. They overflew or couldn't find Howland Island and knowing they were lost and, as per the radio message, commenced flying on a line 157/337 which, because we do not know at what position on their original course they started that, could have found Gardner Island and landed on the reef. They survived there for a short time probably only a few days given the local conditions, possible injury and died. Their remains were dispersed and destroyed by crabs and the weather. The aircraft was washed off the reef and lies somewhere in the water around the island at great depth. This is the TIGHAR hypothesis and they have detailed why they propose it.
3. Having discovered that they had not found Howland Island Earhart and Noonan adopted the contingency plan and flew towards the Gilberts. Somewhere in that area they either ditched in the ocean or came down on or near an island where the wreckage might still be.
4. They instead opted to fly a reciprocal course which eventually led them to crash on New Britain which is the hypothesis based on the testimony of the Australian patrol that claimed to have found an unidentified aircraft wreck in 1945. This has merit also because we do not know precisely where Earhart and Noonan were when they decided they couldn't find Howland. The strength of radio signals is not a precise method of estimating a position by the receiver and Earhart did not, it appears, understand how to operate the DF device they had, or, it appears, knew how long she had to transmit for to enable the receiving station to get a fix.
In summary then I see four possible fates for Earhart and Noonan of which only one can be right. Which is to say the remains of the Electra can only be in one place. As I said the evidence of the post-disappearance messages is at best are problematic because they do not give a location - if genuine they could have come from a reef or uninhabited island in the Gilberts to the north-west as much as from Gardner Island.
I've said it before that the material evidence found on Gardner (shoe parts, compact mirror and that one fragment of aircraft skin) is interesting but are not conclusive. The account by the settlers of the PISS about plane wreckage is interesting but unverified and "Nessie" at present could be anything. The skeletal remains were initially identified physically as a male and probably a person of Pacific Islander heritage - the recent re-identification is not based on the physical evidence and is at best only a hypothesis. After all a male Polynesian castaway on Nikumaroro is as likely, given the documented cases of Pacific Islanders being carried long distances by storms and surviving and one could have suffered that fate and come ashore on Nikumaroro sometime in the early 30s or even late 20s.
So my position in this matter is undecided and will only be decided if material evidence that is irrefutable (skeletal and subsequent DNA or dental verification, the actual wreck of the Electra or parts thereof or something else of similar certainty) is found to indicate their landing and subsequent death on Nikumaroro or elsewhere. Frankly at this stage, given the evidence available, the actual fate of Earhart and Noonan is not yet demonstrated. Everything else, however emotionally compelling, is hypothesis.
All of which aside I wish TIGHAR every success in finding the crucial evidence, as I do to anyone else investigating the fate of the lost aviators.