Rab Wilson, who worked for Ayrshire and Arran NHS Board, asked it for copies of all “critical incident” reviews and significant “adverse event” reports.
The reports are used as a way of investigating incidents, improving safety and patient care and minimising risk.
Mr Wilson turned to Information Commissioner Kevin Dunion after the health board told him it did not hold any critical incident review plans, apart from one it had already given to him.
But when the commissioner investigated, 56 such plans were found on a computer drive.
The NHS board has now been ordered to provide Mr Wilson with a copy of the reports.
A report on the case said: “This decision involves perhaps the most serious catalogue of failings to search for and find information within the scope of a request that the commissioner has ever had to deal with.
“Claims were made to the applicant which turned out to be wrong. Prior assurances were given to the commissioner which turned out to be unjustified. Explanations for the failings were given in the course of this investigation which cannot be relied upon.”
It added: “At the very least, this constitutes a significant failure of records management. Given the nature of the information involving critical incidents and significant adverse events, which needs to be shared professionally for lessons to be learned and for the public to be reassured that action has been taken in response, the information failings may point to wider governance issues which have to be addressed.”
Mr Dunion told BBC Radio Scotland’s Good Morning Scotland: “In the course of the investigation we discovered that over 50 action plans which we had been assured by the health board no longer existed, or were no longer held, were indeed held by them and had not been discovered despite supposedly exhaustive searches and assurances given to my investigators that they could not be found.”
Mr Dunion, who stands down as Scottish Information Commissioner tomorrow, said that when he persisted with his investigation the health board became “extremely irritated”.
He said there was a “degree of incompetence and ignorance” at the health board, “which is not at all satisfactory” but Mr Dunion said the case did not involve a “deliberate cover-up”.
But he added: “Nevertheless I still haven’t got any satisfactory explanation as to why so many reports could not be found by the health authority, despite their searches.”
The commissioner said some authorities needed to “wake up and realise that we’re now seven years into the FoI (freedom of information) regime in Scotland”.
He added: “This is my last-ever decision. I’m leaving office tomorrow. I’m proud of what I’ve achieved so far but clearly there are still instances where authorities haven’t recognised that things like records management and recovering information and making it available promptly when requested is what they are expected to do.”