Orbital radius as a function of time for two merging galaxies (IDs 383325 and 299509) with their associated GCs. The points mark the formation and merger times of the satellites from TNG50. During the initial phase, ex situ GCs orbit within the reference frame of their satellite galaxy until their orbital energy becomes positive (E > 0). Once this condition is met, GCs are transferred to the MW’s reference frame while maintaining the moving potential of the satellite galaxy if it has not yet merged.