IOR Orbital elements
My experience, working with orbit analysts on many satellites, some geostationary, some geosync, some other, these are the most incredible analysts there are. They, by discipline, leave no stone unturned. So I am sure they have analyzed IOR's orbit to the n'th degree and have taken all this into account, along with error bars.
One question I have is how accurate they know the turn-around time for the ACARs TNC on the aircraft, as this device was not designed for ranging. My experience of TNCs are that they are software driven, not hardware, and there could be some uncertainty, on the order of maybe microseconds, depending upon the microprocessor clock speed. A microsecond is ~1000 feet, so I expect the uncertainty = uncertainty time / cos(sat elev), so maybe the uncertainty due to the TNC is on the order of a quarter mile or so, which, again is in the noise?