With just five weeks left in Obamacare's open enrollment period, federal officials Tuesday said new data show about 4 million people have already signed up for new health insurance plans sold under the Affordable Care Act.
But that new benchmark comes with several big caveats that could affect how people view Obamacare's success or lack thereof. Those include questions of just how many of those people actually pay for their first month of coverage, and how far behind enrollments have fallen from original projections.
The Obama administration in the past week has distanced itself from its own original estimates of Obamacare enrollment as it seeks to recast what would constitute success of the health-care reform law.
The new benchmark was disclosed Tuesday in a blog post by Marilyn Tavenner, head of the Centers for Medicare and Medicaid Services.
"Millions of Americans are taking advantage of the new choices they now have to access affordable, quality health care thanks to the the Affordable Care Act," Tavenner wrote. "The most recent data indicate that approximately 4 million people have now signed up for a private health insurance plan through the federal and state-based marketplaces since Oct. 1."
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Tavenner did not disclose how many of those 4 million are known to have paid their first month's premium, which is required for enrollment to be complete. Health insurance experts have estimated that about 20 percent of people who have signed up for Obamacare plans did not end up paying for those plans.
Tavenner's new tally is far below 5.65 million enrollees that the Congressional Budget Office last summer had estimated would have signed up for Obamacare by the end of February.
The CBO also had originally estimated that in February alone, about 1.27 million people would enroll, in contrast to the 700,000 or so people this month assumed by Tavenner's statement Tuesday.
In an interview earlier this month, health insurance consultant Robert Laszewski, president of Health Policy and Strategy Associates in Washington, D.C., had told CNBC.com, "I'm hearing the enrollment in February is falling off significantly."
The CBO's estimates were made before the launch of the federally run HealthCare.gov Obamacare exchange, which was essentially crippled for its first two months of operation by hundreds of software flaws which dramatically hampered enrollment in the 36 states that it serves.
Several state-run ACA exchanges, including Maryland and Oregon, have also suffered severe problems with their websites, which have been blamed for dampening enrollment.
The CBO had originally estimated that a total of 7 million people would enroll in Obamacare plans by the end of open enrollment on March 31.
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But implicitly acknowledging that the outlook had changed because of the technical problems with some of the exchanges, Vice President Joe Biden last week said, "We may not get to 7 million, but if we get to 5 or 6 million, that's a hell of a start."
And on Tuesday, Tavenner's boss, Health and Human Services Secretary Kathleen Sebelius, suggested that the Obama administration had never adopted the CBO's estimates as its own.
"First of all, 7 million was not the administration," Sebelius said during an appearance on HuffPost Live. "That was a CBO, Congressional Budget Office, prediction when the bill was first signed. I'm not sure where they even got their numbers. Their numbers are all over the board. The vice president has looked and said it may be closer to 5 to 6."
However, Tavenner herself, in a Sept. 5 memo to Sebelius had used the total 7 million estimate in a table entitled "Projected Monthly National Enrollment Targets for Health Insurance Marketplaces."
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Weeks later, in a Sept. 30 interview with NBC News on the eve of the launch of the Obamacare exchanges, Sebelius herself said, "I think success looks like at least 7 million people having signed up by the end of March 2014."
March 31 is the deadline by which most Americans must have some form of health insurance, or face a tax penalty next year totaling 1 percent of their adjusted gross income, or $95, whichever is greater.
—By CNBC's Dan Mangan. Follow him on Twitter @_DanMangan.