Blacksheep`s commentary makes a lot of sense in setting out the limitations of satcom data analaysis carried out by INMARSAT.
INMARSAT announced that after six complete handshakes recorded at the ground station following ACARS, the a/c`s operational comms sytem stopped sending messages. INMARSAT was then able to calculate range of a/c from sat and time taken for signal to be sent and received. They then generated the well published Northern and Southern Corridors. Which seemed to cover a large chunk of mother earth and water. So got their heads back down and developed a second innovative technique which took into account the Doppler effect, which we all know from watching ambulances, police cars and for train spotters, locos. They analysed the frequency that the ground station expected to recieve and the one actually measured, which they told all is called the Burst Frequency Offset. They then checked this prediction with six other B777 a/c flying on the same day in various directions which resulted in a good match with the Southern Corridor. So off went all the troops in that direction.
So it would seem to me at least, that the whole thing is built on much theory and little hard fact. Until such time when some debris is washed on someone`s shores nothing will be known.