“But also in the US, pilots have the ability to erase the CVR once at the gate—and it’s certainly possible this occurred before MH370 went into the ocean.”
WOW (weight on wheels) switches have to be made to allow the CVR to be erased. Not possible in flight.
If the FDR (Flight Data Recorder) is ever found and gotten into the hands of competent people, we will know the story.
Two big ‘ifs’ in that sentence.