Content of engine monitoring system messages ?
Some of the B777 messages have lat/long and Alt in them and some do not. However the spatial data refers to where the engine snapshot was taken, not where it was transmitted. The messages sent back to RR would have been just off the runway to reflect take off power and possibly, not definitely, at a nominated height to reflect climb power.
If something had malfunctioned or there was an out of spec reading then this would have triggered a different report. A lot has been made of the ACARS system being off, but unless there was something wrong with the aircraft the system would have created a snapshot when it was supposed to and transmitted it when it could.