According to a review released by the California Department of Managed Health Care (DMHC), 90 percent of California insurer reports on which providers were in their network contained inaccurate information.

This report didn’t deal with the directories of providers used by patients, which have their own accuracy problems. It was assessment of compliance reports submitted by insurers to DMHC in 2016 about how long patients had to wait for doctor’s appointments and plans’ rosters of providers.

“Timely Access Compliance Reports submitted by health plans for 2015 contained extensive and unacceptable data inaccuracies regarding network providers and voluminous data errors regarding rates of compliance,” the report said. “In addition, the reports illustrated numerous instances in which health plans failed to follow the mandatory methodology published by the DMHC.”

Major insurers had some of the greatest number of errors, according to the report. For example, Aetna’s compliance data contained “significant inflation in number of specialists” by counting the same cardiologists in a single county over 160 times. Overall, the data it submitted had over 20 percent variance for including specialists and primary care providers which weren’t in their networks.

Those kinds of errors, the report said, make it “virtually impossible” to assess whether plans are providing “timely access” to care for patients.

“The DMHC cannot determine (or report to the public) how many health plans did (or did not) comply with the appointment availability requirements, due to the failure by nearly every plan within the industry to submit accurate compliance data,” the report said. “This undermines the purpose of the Timely Access laws and regulations, which require an annual review of health plan networks for the express purpose of determining whether consumers can see their doctors to obtain medically necessary services on a timely basis.”

Insurers were given a chance to rectify data errors, according to DMHC, which said it issued nearly 150 comments to plan about inaccuracies discovered in the review. In most cases, however, plans failed to make any corrections.

The department said it will investigating or potentially fining plans which overstated their networks. Penalties have been handed down before, with Blue Shield of California being fined for $350,000 and Anthem for $250,000 for similar violations in 2015.