But 1912/22 'authorities' are irrelevant, Richard, because no-one denied both the de facto & de jure authority of UN to make the decision in 1947. Can't see why you keep dragging the, by then long superseded, Ottoman/Turkish interest, which had by then long ceased to be a factor, into the discussion at all. It seems to be some redcondite, arcane, mnemonic thought-process of your own.

~~~"both recognised by the UN and (a separate issue) by each other." ~~~

But that's the bugbear, Richard. The Palestinian entity wants statehood recognised by membership of UN, without any undertaking to recognise Israel's {a member since 1949} right to existence. They are not, surely, 'separate issue[s]'? You go on to admit so yourself ~
"I don't offhand see how Palestine could (lawfully) continue its opposition to the existence of a state of Israel if it was a member of the UN (because it WOULD then have "joined the club")".

But they [the Palestinians] nevertheless seek membership without any such undertaking.

There's the rub. Do you really not get it?