I have said this once before, however I will say it again. The validity of the radio messages is as much dependent on Nikumaroro being demonstrated to be Earhart's landing spot as is their validity as genuine radio messages which reflect that situation.
Now while that sounds awfully obvious it isn't really because we have a situation where each of the components of the Earhart/Nikumaroro hypothesis have to be tested individually as they are all dissimilar phenomenon, each with their own individual set of physical and psychological features, in the chain of circumstances that creates the hypothesis.
Now we are all aware that the process isn't aided by the hoaxes, the utter disregard for the urgency of accurate information by the radio and print media (nothing new there), the misunderstandings of the March of Time program and the general level of background radio noise that is bouncing around at the time. Furthermore their validity is not helped by the need to second guess every part of Betty's notes (or anyone else's for that part) to say what the Nikumaroro hypothesis demands rather than what the notes actually say. The moment when you start reading a purported eyewitness account and have to start saying "Well this is probably what she heard ..." rather than just accepting that she heard what she said she heard is the moment you have departed company with logic and are creating a hypothesis out of whole cloth. Has anyone considered seriously that what she noted was what she heard, which means why on Earth is Amelia Earhart rabbiting on about a suitcase while claiming that Fred's getting stroppy. If that doesn't indicate a hoax by someone with a mordant sense of humour nothing does.
As for the need of the hoaxers to transmit some actual locations, they have no need because they only want to fool the audience and have a bit of sick fun. While on the other hand if Earhart or Noonan is actually responsible for some of the messages then they go out of their way not to tell us anything - in other words on the one hand you have sick idiots and on the other needy idiots who don't tell us where to find them. And people wonder why some of us view the radio traffic with a raised eyebrow.
The Navy dutifully does a search - one of the islands is Nikumaroro and they don't see anything at all. Now some 75 years later we are second guessing them and saying well perhaps the surf was up and the wreckage was probably hidden, and the observers didn't know what they were doing or Amelia and Fred are passed out under a tree and can't be seen, or they wave but no one sees them etc. etc. etc. Wonderful excuses to explain away the very real possibility that they weren't on Nikumaroro to be seen. Calm down everyone, that's just silly old me being logical and looking at the evidence.
If TIGHAR find the wreck or bits of it, or they find something quite incontrovertibly linked to the pair on or near Nikumaroro then that will validate some small part of the radio traffic (only that however which can be 100% linked to the island's location) - but as no one has found that vital evidence then the radio messages are really about as useful or as uncontaminated as the other ethereal medium, the psychics who plagued George Putnam with messages from the other side.