Hospital doctor's a record holder (9)

I believe the answer is:

registrar

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'hospital doctor's' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for registrar that I've seen before include "Administrator responsible for records" , "Wedding recorder" , "University official" , "Record keeper - hospital doctor" , "Official recording births, deaths and marriages" .)

I've seen this clue in The Guardian.

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