If WGS84 was correcting for tectonic drift it would imply that the coordinates of the terrestrial fixed points used to compute the reference meridian never chan

If WGS84 was correcting for tectonic drift it would imply that the coordinates of the terrestrial fixed points used to compute the reference meridian never change under WGS84. Rebasing the coordinates of terrestrial fixed points prior to calculation disregards tectonic drift in the reference meridian calculation, it doesn’t correct it. It is a noise reduction exercise to minimize the influence of plate tectonics on meridian drift. The meridian uses non-terrestrial fixed points too that don’t have a concept of tectonic drift (but may introduce their own idiosyncratic sources of noise). Basically, these are corrections to their “fixed points” to make them behave more like actual fixed points in the reference meridian model. It doesn’t eliminate tectonic drift effects when using coordinates in that spatial reference system.