'Ping' data is to all intents the same as 'active connections'. So long as your phone is switched on it is permanently connected via a mast/base station to the network. So there is, therefore, a permanent live connection (although no actual call) to the mast from the phone sending out an "I am here, anybody there" ping which is picked up by the nearest available mast and answered with a "yes, I'm here, who are you?"
So when switched off, the phone is absent from mast records, but that is not the same as saying the phone was absent from the area - absence of evidence etc etc...
What we are saying is we only know PJ have data for actual voice or SMS connections to the relevant towers.
We don't know if they have any ping data - the handshake process you describe is not a permanent connection. Rather the phone connects with the nearest/best tower periodically - so the network knows where the phone is to allocate resource to it.
So if PJ had ping data, they would know when the phone first connected to the PdL tower, and when it disconnected - e.g. moved too far away or was turned off.
I guess @Janosch is correct that based on what was disclosed in the PJ files, they don't have the ping info, or triangulation.
This is not too unusual. In the McStay case, (2010 murder) the prosecution also did not have ping, and only basic azimuth.