The president and Sylvia Burwell, Health and Human Services secretaryTop: Susan Walsh/AP, Bottom: J. Scott Applewhite/AP

It turns out the Affordable Care Act didn't meet its first-year goal of enrolling 7 million Americans in private insurance plans after all.

The Obama administration disclosed on Thursday that it mistakenly included about 380,000 dental plans in the 7.3 million people who enrolled through state and federal exchanges for 2014. With those dental plans subtracted and including updated data, the Department of Health and Human Services said the number of enrolled Americans as of October 15 was 6.7 million.

The department's secretary, Sylvia Burwell, called the mistake "unacceptable" in a Twitter post and later in a Facebook chat she conducted with MSNBC's Chris Hayes. "This mistake was unacceptable," she wrote.

"I will be communicating that clearly throughout the department. While we understand some will be skeptical, our clarity that this is [a] mistake and the fact that we have quickly corrected the numbers should give people confidence. It is important to continue to focus on the fact that millions of Americans are getting affordable health care."

The news that the Obama administration had met—and seemingly exceeded—the 7 million target earlier this year was seen as a surprising comeback story following the disastrous, error-filled launch of Healthcare.gov and several state exchanges.

Bloomberg first reported the snafu Thursday, citing an analysis by Republicans on the House Oversight and Government Reform Committee. The office of Majority Leader Kevin McCarthy said in a statement that the administration "increased their numbers artificially in order to reach their enrollment goals."

"It seems that this administration’s habit of obfuscation continues long after the failed health care law has passed."

It is the latest in a series of troubling developments for the 2010 law, as the Obama administration prepares to defend it once again against a Supreme Court challenge and tries to combat year-old accusations from economist Jonathan Gruber that officials knowingly misled the public about its impact. The beefed-up Healthcare.gov has had a smoother launch in its second open enrollment period that began on November 15, but the Obama administration has already dropped its projection for how many people will sign up in year two. Officials now believe about 9.1 million people will enroll, down from the 13 million that the Congressional Budget Office had previously estimated.

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