Your friend at FW should have explained it to you, reference
comment #170and their use of the Standard 29.92 altimeter,how that affects the Mode C readout of the aircraft's altitude,
It comes from the data received from that aircraft's mode C.
And based on what's on that Flight Track Log, the data was not continuously transmitted twice a minute.
Sometimes it was received only once a minute. or not a all for over a minute ( 05:33-05:40 ).
Could that spotty reception have been because of the weather?
Let me spell it out for you, mister.
1. I KNOW THAT 29.92 IS USED IN CLASS A AIRSPACE.
2. I KNOW THAT IF YOU DESCEND FROM FL180 YOUR ALTIMETER MUST BE RESET TO LOCAL CONDITIONS, PROVIDED BY CENTER.
3. I KNOW THAT TO GET CLEARANCE TO LAND YOU HAVE TO HAVE THE CURRENT ATIS INFO CODE.
4. SCREW FLIGHT TRACK...THEY WERE NOT THE PIC.
5. What ARTCC do you work out of?