When did the UN start to use that terminology?
It appears that the term started being used, informally, around 1989, and formally in 1998.
This memo from 1988 calls them "West Bank and Gaza" and "occupied territories."
In 1989, we see simply "occupied territories."
Even this 2000 Security Council resolution refers to "territories occupied by Israel."
While many PLO letters to the UN refer to "occupied Palestinian territory" the UNGA did not seem to give it that proper name, using capital letters, until much later - in 1998.
In December of that year:
At its 81st plenary meeting, on 7 December 1998, the General Assembly, on the proposal of Djibouti, Egypt, Jordan, Kuwait, Mauritania, Oman, Tunisia, Yemen and Palestine, A/53/L.65 and Add.1. requested that the Secretary-General should continue to use the term Occupied Palestinian Territory, including East Jerusalem, when appropriate, in accordance with General Assembly resolutions, in relevant reports to the Assembly, including the report under the item entitled Assistance to the Palestinian people, bearing in mind the need to take account of future relevant Assembly resolutions and progress in the Middle East peace process.So the term "Occupied Palestinian Territory," or "OPT," was only formalized in the UN in 1998 - well after Oslo.
Here is where it gets interesting.
The UNISPAL set of documents relating to Palestine gives titles to each memo that comes out of the UN. The titles in UNISPAL's index have nothing to do with the actual titles of the documents.
And whoever gave these documents their titles deliberately uses the term "OPT" in documents that were written many years before the UN adopted that increasingly incorrect term!
Some of them from 1980:
The UN is deliberately rewriting its own history to make it appear that the term "Occupied Palestinian Territory" has been used forever, when in fact it is of relatively recent vintage.
This is most unethical and an insult to people who want to use the UN site for historical research. It shows a blatant disregard for facts and history.
It is, effectively, a UN-sanctioned mass rewriting of its own records.
Another interesting find.
This 1983 resolution says:
Bearing in mind the provisions of the Geneva Convention,The UN is saying here that the Geneva Conventions apply because the Arab states whose territories are occupied are parties to Geneva, and therefore Israel is considered to be occupying them. Geneva only applies when both parties are High Contracting Parties of the Convention itself.
Noting that Israel and those Arab States whose territories have been occupied by Israel since June 1967 are parties to that Convention,
Taking into account that States parties to that Convention undertake, in accordance with article 1 thereof, not only to respect but also to ensure respect for the Convention in all circumstances,
1. Reaffirms that the Geneva Convention relative to the Protection of Civilian Persons in Time of War, of 12 August 1949, is applicable to Palestinian and other Arab territories occupied by Israel since 1967, including Jerusalem;
But if the territories are "Palestinian," and "Palestine" is not a party to the Convention, then that preamble makes no sense!
Indeed, the UN no longer uses that argument anymore, simply declaring the territories to be "occupied" by assertion.