Upset at late SOS; it means ship has sunk (4,2,3)

I believe the answer is:

lost at sea

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'ship has sunk' is the definition.
I can't tell whether this defines the answer.

'upset at late sos' is the wordplay.
'upset' indicates an anagram.
'at'+'late'+'sos'='atlatesos'
'atlatesos' anagrammed gives 'LOST AT SEA'.

'it means' acts as a link.

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I've seen this clue in The Irish Times.

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