Errors that led Nielsen to restate Fox Super Bowl audience numbers are also having broader impact, leading to reprocessing of data in 12 local markets and raising questions about how much value the company’s recently restored Media Rating Council accreditation brings.

Nielsen sent a letter to clients May 2 that it will reprocess local TV data in 12 of its 44 Portable People Meter markets across the U.S. after finding the error that led to undercounting out-of-home viewing of the Super Bowl broadcast also had affected broader local ratings. Those markets include Chicago, Cincinnati, Detroit, Houston, Kansas City, Memphis, Miami, Milwaukee, Norfolk (Virginia), Pittsburgh, Providence (Rhode Island) and San Antonio.

Nielsen will reprocess local ratings data for those markets from Jan. 9 to March 30. Nielsen has not indicated any broader restatements are coming on national ratings.

But some national network executives question whether that error, as well as another involving audio encoding that mistakenly moved about 1 million viewers from Fox properties to the NFL Network for the Super Bowl, also affected in-home and out-of-home viewing for national programming, particularly sports.

While big in absolute terms because it involved the Super Bowl, each error represented less than 1% of the average minute audience for the game, so might easily be missed for the vast majority of lower-rated programming.

Collectively, however, the adjustments Nielsen made, were they to apply across a U.S. TV market estimated by various researchers at $65 billion to $68 billion, would come to more than $1 billion.

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But at least for NBCUniversal, the reported errors point to bigger issues and raise questions about the value of Media Rating Council accreditation, which Nielsen has touted since accreditation for its national TV ratings was restored last month after a 19-month hiatus.

“Nielsen's recent errors reaffirm our position on why a multi-currency framework is imperative for advertisers,” said an NBCU spokesperson in a statement. “These errors also call into question the validity of the re-accreditation process which, after 25,000 hours of audit, failed to detect basic processing errors that could occur during the biggest TV event in the world. Publishers and advertisers need the most accurate read on consumer behavior, because accurate measurement is critical for our industry’s future.”

Nielsen has rejected participating in a request for information and certification process from the Joint Industry Committee, which includes NBCU and most other major network players in addition to Roku and agency representatives. And, following an exchange of letters and talks, the remaining sticking point for the company participating with the JIC is its demand that all JIC-certified measurement companies be MRC accredited, not that they simply seek accreditation, as required by the JIC, according to people familiar with the matter.

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Beyond the PPM coding issue, which has been fixed, audio encoding is something network clients enable to allow Nielsen to measure, a Nielsen spokesman said, adding that it’s up to the MRC to discuss that process with publishers.

He said the PPM issue was unrelated to accreditation, but that “MRC accreditation requires us to restate and disclose when errors are uncovered, which supports transparency and trust in the media industry.”

The accreditation process, “is a comprehensive review of all components, methodologies and processes,” he said, to ensure that a company “meets a rigorous set of standards that yield a consistent set of data that the user can rely on as representative of the general universe.”

The MRC process dictates that material errors are disclosed to customers, a spokesman for the MRC said. “That’s why you see Nielsen and Comscore occasionally making these kinds of disclosures,” he said. “Other (non-audited) services don’t generally do this for the customer base. It’s not because they don’t make mistakes.”