Had been a forger, one didn't let oneself forget (4,1,4)

I believe the answer is:

made a note

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'forger one didn't let oneself forget' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'had been a' is the wordplay.
I cannot quite see how this works, but
'had' could be 'made' ('make' can be a synonym of 'have') and 'made' is found in the answer.
'a' could be 'an' and 'an' is located in the answer.
This may be the basis of the clue (or it may be nonsense).

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I've seen this clue in the Evening Standard.

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