Must those who don't know the score do so? (5-4)

I believe the answer is:

sight-read

This could be a double definition.

'must those who don't know the score' is the first definition.
I know that 'score' relates to this answer.

'do so?' is the second definition.
'sight-read' can be an answer for 'do' (sight-reading is a kind of doing). I am not sure about the 'so?' bit.

(Another definition for sight-read that I've seen is " Interpret music without preparation".)

I've seen this clue in The Times.

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