Legally acquire scribes for an auditor (2,6)

I believe the answer is:

by rights

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'legally' is the definition.
Both the answer and definition are adverbs. Perhaps you can see an association between them that I don't see?

I don't understand how the remainder of the clue works.

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(Other definitions for by rights that I've seen before include "Legitimately" , "If things were fair" .)

I've seen this clue in The Times.

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