“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.
Reportedly, the CVR only records the most recent two hours. That would mean, when and if it is found, it will likely have close to two hours of engine drone, followed by some minutes of relative quiet and a big splash. The "good parts" — "Allahu akbar!", [banging sound] "Open up, have you lost your mind‽" — will have been overwritten. And they'll have to rely on the FDR's data to suss out what probably happened.