The question is unambiguous: was it just NHS Lothian that manipulated its waiting list figures to make them look better than they were, or were other health boards guilty too?

The answer provided in an Audit Scotland report today is much less clear.

There is no evidence that other health boards fiddled the figures to the same extent as NHS Lothian. However, NHS Tayside has already confessed to serious mistakes in data.

An internal audit found patients there being marked as "socially unavailable" for treatment, without the individuals being contacted, just at the very moment when the patients were going to breach target times. This echoes aspects of the Lothian story.

Patients in Tayside were also marked as medically unavailable for treatment, when actually the patient was fit enough, it was just the necessary equipment was not ready in the hospital. Even more were recorded as unavailable simply because the consultant had told them they could not be treated in time.

In other board areas Audit Scotland has found "a small number of instances in which unavailability codes were used inappropriately". Its report said: "The limitations of waiting list management systems and the lack of evidence in patient records mean it is not possible to determine whether these instances were due to human error, inconsistent interpretation of the guidance, or deliberate manipulation of waiting times."

Health Secretary Alex Neil welcomed the findings saying: "There are no examples of manipulation of the figures like those found at NHS Lothian."

However, Jackie Baillie, health spokeswoman for Scottish Labour, said the report made it clear "hidden waiting lists were widespread".

The one conclusion that is not in dispute is that the different information technology systems used for managing waiting times were not good enough, and have made proper policing impossible.

Asked if manipulation was widespread, Audit Scotland points to the graph that shows use of social unavailability codes dropping in health boards around the country at the same time as the manipulation in NHS Lothian was exposed. This might seem to speak for itself.

Mr Neil attributed this trend to health boards updating their waiting times databases and removing patients who should not have been listed, such as those who had died. He also said an increase in hospital capacity had allowed more patients to get appointments which suited them.

Audit Scotland's investigation does not explore these explanations – but where its auditors observed unusual patterns in waiting list data it probed further and report what it found.

The single highest use of social unavailability codes uncovered was at the Western Infirmary in Glasgow in early 2011. There 70% of the patients on the waiting list for orthopaedic treatment were coded as socially unavailable. In addition, 40% of patients waiting for ophthalmology outpatient appointments at the Southern General were down as unavailable. Finding out why patients were given such codes has been particularly difficult in GGC where the computer system does not retain old data and there is more than one data system in use and the contract with one supplier has come to an end.

In a statement, NHS GGC explained: "Within NHSGGC a number of orthopaedic and ophthalmology patients turned down offers of treatment in one of our hospitals within the GGC area in favour of waiting for either a specific clinician or because they wanted to have their procedure in a specific hospital. Under the terms of the National Waiting Times Guidance, a patient, could in these circumstances, be removed from our waiting list and returned to their referring clinician.

"However, instead of doing this we tried to accommodate the wishes of these patients by not removing them from list but instead retaining them on the list of their requested hospital or clinician and advising them that their waiting time would not be within the national guarantee. They were coded as socially unavailable because it was the only code which was not related to a 'medical' reason as to why surgery should not go ahead."

Use of social unavailability codes was also notably high in NHS Grampian, according to the report. In June 2011, more than half the waiting list for orthopaedic surgery was marked as socially unavailable. There were also times when a lot of patients seemed to have multiple periods of social unavailability recorded. Last August, 300 patients had four or more periods included in their wait. Perhaps more worrying still in the space of a couple of hours, the auditors found NHS Grampian staff marked 171 patients as unavailable, with all those patients becoming available again on the same date. The health board told them it was aware of the issue and said it had exposed a need to train staff as the wrong code had been used by mistake.

Information about why patients were given codes was much better in Forth Valley than other health board areas. It had its own code which described patients who were aware they were going to wait longer than the target time for treatment and were willing to do so. In terms of its official performance statistics these people were described as socially unavailable and again the proportions were high in comparison with other health board areas.

Some patients in this patch had been marked as socially unavailable indefinitely. In a sample of records checked there were two patients recorded as unavailable for more than a year.

Staff in Lanarkshire had their own catch-all code labelled "patient requests suspension". Staff said this was often used for people wanting to be seen at a particular hospital. During the period examined 21,699 transactions on its waiting times database involved this code.