The author seems to treat the atmosphere as a, well, sphere. It isnt. It is not of equal depth at all areas. As starlink (and every other sat) only travels in part of the atmosphere each day they cannot measure the entire atmosphere. So you measure a thousand starlinks to get an average. Ok, but a significant bulge on one side of the planet will slow all sats, giving the false impression of a homegenous trend. So you have to track very specific sats in very specific survey orbits... but also update that list as the orbital shell rotates around the earth. It is a very complex problem.
Link to article: https://www.spaceweather.com/starlink/starlink_drag_explaine...
The author seems to treat the atmosphere as a, well, sphere. It isnt. It is not of equal depth at all areas. As starlink (and every other sat) only travels in part of the atmosphere each day they cannot measure the entire atmosphere. So you measure a thousand starlinks to get an average. Ok, but a significant bulge on one side of the planet will slow all sats, giving the false impression of a homegenous trend. So you have to track very specific sats in very specific survey orbits... but also update that list as the orbital shell rotates around the earth. It is a very complex problem.