The mandate was created in February 1993. It goes back nearly three decades, and it even predates the Oslo accords, when the Palestinian authority entered Ramallah, Nablus, Hebron—cities that they controlled—as well as Jenin and Bethlehem, and Hamas-ruled Gaza. The mandate predates that.
It's the only mandate that looks at one side. The other special rapporteurs, whether it's on Sudan or others, will look at all sides, and will look at the human rights situation in a region. This one, as the current mandate holder has acknowledged, only looks at one side. It states:
The mandate calls on the Special Rapporteur: (a) To investigate Israel's violations of the principles and bases of international law....
It does not look at abuses by the Palestinian Authority.