Added aliases to datum 6298, CRSs 4298, 29873 29849-50 and tfms 1228 1592 1615 1852. For datum 6298 also added remarks regarding 1968 extension. For CRS 29871, in remarks added cross-reference to 29872. For CRS 29872, amended scope. For CRS 29873, amended scope and remarks. For tfm 1592, deleted remarks. For tfm 1615, amended remarks.