Book initially ignored irrefutable data (4)

I believe the answer is:

acts

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'book' is the definition.
(book of the Bible)

I cannot understand how the remainder of the clue works.

(Other definitions for acts that I've seen before include "Fifth book of the New Testament" , "Dramatic parts" , "individual performers in a show" , "Takes steps" , "Pieces of legislation" .)

I've seen this clue in The Independent.

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