About the satellite pings
I note many posts referring to earlier pings and asking the question why no information has been released concerning anything other than the “last ping.” Maybe I can shed some light on this.
Summary
1) It is most unlikely that data relating to anything other than the most recent ping would be retained onboard the satellite, and
2) Each ping must necessarily contain an unique identifier.
Communication satellites generally use time division multiple access (TDMA) to enable them to service many “clients” simultaneously. This works as follows: the satellite allocates time slots to each client for them to uplink their data, so that in normal operation client A transmits a brief burst of data then Client B, client C and so on. The whole sequence repeats many times per second in so-called frames. For this to work, the sat’ needs to keep a record of all its potential clients and the time slot(s) allocated to each one. This is the TDMA scheduling table and it is maintained by the satellite’s on-board computer.
Periodically, the satellite broadcasts a channel access frame, inviting any new client wanting to use the satellite’s services to identify itself and the services it wants to access. The timing of the replies received during the channel access frame enables the satellite to work out the most suitable time slot(s) to allocate to that client. Note that in doing so, the satellite has implicitly calculated the round-trip time for radio waves to that client.
Once a client (aircraft, sat-phone, etc.) has established channel access it periodically pings the satellite to check its time slot allocations. (Hello this is client XYZ. My time slot is 36ms after the frame. Is that still OK?) If the client has moved significantly, the satellite may notice the timings have changed and update its TDMA tables with a new time slot for that client. Note that all of this TDMA stuff is merely to maintain access to the satellite if needed and has nothing to do with actual data transfer, which is negotiated separately as and when needed.
The operative word is update in that paragraph. When the tables are updated, previous values are overwritten and lost. There would be no reason to log or down-link all the technical details of the TDMA protocol as that information has no commercial value to the satellite operator.
When a client falls silent, its entry will remain in the TDMA tables until expunged to make room for a new client. It would appear that Inmarsat were able to interrogate their bird before this happened and down-link the data for MH370. Unless the satellite was logging useless, out-of-date information, this record would contain only the most recent ping data.