Here is a description of where the Geo-Data is comming from as far as I still could remember:

• The data of the reference stations like the IGS Network, UNAVCO, CORS, and Benchmarks from Kansas, Bolivian Salt Flats, Erie Canal, are publicly available (cm accuracy).
• The data from the Causeway at Lake Pontchartrain, the Rainy Lake experiment, the Great Salt Lake Desert Rte 80, Mason Dixon Line are measured with professional Differential GPS equipment by Jesse Kozlowski to 5 cm accuracy.
• The flight data was recorded with mobile GPS trackers by Wolfie (Dubai to LAX, Syndney to Dallas, Sydney to West Coast) and GreaterSapiens (flight around the world, San Francisco, Sydney, Perth, Antarctica, Perth, Sydney, Johannesburg, GRU, BOG, SAL, San Francisco). The pilot Wolfie could also provide some cockpit data like altitude, heading, speed.
• Flight data QFA14 (Buenos Aires to Darvin) either from Wolfie or from FlightRadar24, not sure
• The data from the sail drone around Antarctica is from the corresponding Website (onboard GPS tracker)
• The data from the VandeeGlobe sailing race are from the corresponding Website (onboard GPS trackers)

The reference stations are measuring raw GPS coordinates in ECEF cartesian coordinates. They are the most accurate measurements of earth to better than cm accuracy.

The data from Jesse are collected using Differential GPS equipment to better than 5 cm accuracy.

The data recorded with GPS trackers were given in KML files exported from the trackers. The KML files contain processed GPS positions, i.e. in latitude/longitude/elevation rather than the raw ECEF coordinates. I converted them back to ECEF coordinates for my App. Their accuracy is the common GPS accuracy, in the meter range or better.

Some flight data from the KML files contain additional data like speed, altitude, heading and timestamps. You can inspect this files with my App at the page

 GPS Flight Data and the Shape of the Earth