Fails to count ducks — around ninety (8)

I believe the answer is:

excludes

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'fails to count' is the definition.
I can't judge whether this definition defines the answer.

'ducks around ninety' is the wordplay.
'ducks' becomes 'eludes' ('elude' can be a synonym of 'duck').
'around' means one lot of letters goes inside another.
'ninety' becomes 'XC' (Roman numerals).
'eludes' going around 'xc' is 'EXCLUDES'.

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I've seen this clue in The Times.

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