Amnesty International and calculating execution rates in Middle East countries

So we have discovered (see post about Liz Sly from yesterday) that the methodology of Amnesty International allows it apply an exclusive and peculiar method only to Iran: that in all other Middle East countries (like Saudi Arabia and Jordan) it basically adheres to official number of executions but only in the case of Iran it adds additional numbers of executions that it says it had obtained from "reliable sources" (read Tel Aviv).  But how come Amnesty does not have reliable additional number of executions beyond the official figure in Saudi Arabia? Unless it believes that the Saudi regime, being the favored Western democracy in the Gulf, would never tell a lie?