Blood group recorded in error (4)

I believe the answer is:

typo

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'error' is the definition.
(typographical error)

I cannot understand how the remainder of the clue works.

(Other definitions for typo that I've seen before include "Mistake in printed matter, in short" , "Printer's error" , "Literal error in printed matter, in short" , "Keyboard slip-up" , "False character" .)

I've seen this clue in The Times.

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