Unknown journalist's letters found finally (4)

I believe the answer is:

zeds

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'letters found finally' is the definition.
I can't tell whether this definition defines the answer.

'unknown journalist's' is the wordplay.
'unknown' becomes 'z' (algebra).
'journalist's' becomes 'ed's' (short for editor).
'z'+'eds'='ZEDS'

Can you help me to learn more?

(Another definition for zeds that I've seen is " Sleep - last letters".)

I've seen this clue in The Independent.

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