WASHINGTON — The benefits backlog at Veterans Affairs is worse than leaders there have acknowledged, according to a new investigation from the department’s top watchdog.

In a report released Monday, the VA inspector general found tens of thousands of benefits cases omitted or ignored by department officials that “significantly understated the number of claims awaiting decisions for over 125 days.”

Investigators estimated that the reported backlog only covers about 79 percent of relevant cases, with a host of others misclassified, mistakenly excluded and, in some cases, only acknowledged as overdue after the files had finally been processed.

In response, VA officials said they are “reviewing how best to supplement or adjust reporting on the rating-related backlog.” New training and standards are expected to be put in place by the end of this year.

The VA claims backlog was a major scandal during President Barack Obama’s administration, as frustrations grew over the slow pace of VA’s ability to handle an ever-growing number of disability claims.

The backlog — the number of ratings cases that took more than 125 days to complete — swelled to more than 611,000 in March 2013 before being drawn down to about 70,000 in September 2015. Officials at the time credited a combination of more staff hires, new processing systems and new electronic medical records for the drop.

Former VA Secretary Eric Shinseki had made a public pledge to bring the backlog down to zero before 2016, but officials later acknowledged that was an unrealistic and potentially problematic goal. Some claims take longer than four months due to complexity or updated paperwork.

The backlog has hovered between 70,000 and 100,000 cases each week for most of the last three years, even as the total number of claims applications have continued to rise. Last week, the backlog was 86,001 cases, according to VA records.

But the inspector general, citing a review of cases from the first six months of 2016, said about 63,600 overdue cases that required ratings decisions were left out of those records for unclear reasons, and nearly 10,000 more were incorrectly recorded by staff.

In some instances, VA staffers acknowledged lengthy waits on cases only after the files were finalized months later.

The report found that while the average days pending for basic disability claims now sits at less than 90 days, other more complex cases are taking more than 200 days to complete.

VA officials said much of the claims backlog rules and oversight has remained unchanged since 2009, and officials are reviewing other potential updates by the end of the year.

The full report is available on the VA inspector general’s website.