That NYT article citied a telling quote.
One uncertainty about the flight involved when it disappeared from radar and how quickly the search began in the Gulf of Thailand. Malaysia Airlines said that the plane took off at 12:41 a.m. Malaysia time, and that the plane disappeared from air traffic control radar in Subang, a suburb of Kuala Lumpur, at 2:40 a.m.
That timeline seemed to suggest that the plane stayed in the air for two hours — long enough to fly not only across the Gulf of Thailand but also far north across Vietnam. But Mr. Lindahl of Flightradar 24 said that the last radar contact had been at 1:19 a.m., less than 40 minutes after the flight began.
The FR24 people should know their data well enough, why everyone else didn't is a mystery. At least that confirms a splash site in the entrance to the Gulf of Thailand - best news on a bad situation.