Sheriff Grahame Ritchie Fleming was unable to view footage of the last hours before prisoner Gary Andrew Traynor, 45, was found dead in his cell on 15 March last year.
A DVD backup ends at 6:30pm, shortly before Mr Traynor's body was discovered, and the original footage was routinely wiped after 30 days.
Sheriff Fleming instead had to rely on the testimony of prison guards and investigating police officer DC Phillip Richards, 41, during his Fatal Accident and Sudden Death Inquiry at Livingston Sheriff Court last week.
A post-mortem examination determined that Mr Traynor, a heavy smoker with a history of drug and alcohol abuse, died from "ischaemic heart disease".
Sheriff Fleming said: "Where there is a death in custody and footage is in existence, this should not be overwritten until permission to do so is given by the Procurator Fiscal."