"why the PLO was established in 1964...prior to any "occupation" by Israel?" The sovereign boundaries of the state of Israel were declared on 14 May 1948. These legal boundaries have never changed. You are confusing the armistace lines from 1949 which are not the legal boundaries of the state. Hence, Israeli occupation started as soon as Israeli forces controlled any area outside the boundaries of the sovereign state. Please see 'Plan Dalet'
Palestinians, IDF clash in Jalazone after funeral of teen killed by IDF on Friday (Haaretz)
from the article: U.S.-Israel tensions ignite 'war of words' among Israel lobbies