Complex sentence: In 1976 the IAU chose a radius of, later refined by the IUGG to and adopted in WGS-84, though the yet more recent IAU-2000 has retained the old IAU-1976 value.
Split into simpler sentences: In 1976 the IAU chose a radius of (codified as the IAU-1976 value), later refined by the IUGG to and adopted in WGS-84. Despite this change, the yet more recent IAU-2000 retained the old IAU-1976 value.