President Obama’s claim last spring that 8 million people had enrolled in ObamaCare recently got a significant downgrade from the head of the agency overseeing the plan.

Marilyn Tavenner, administrator of the Centers for Medicare and Medicaid Services, told a congressional committee that "as of August 15, this year, we have 7.3 million Americans enrolled in Health Insurance Marketplace coverage and these are individuals who paid their premiums."

A key part of her statement was Tavenner's reference to those who paid, because just signing up isn't enough to be counted as enrolled.

As Doug Holtz-Eakin, former director of the Congressional Budget Office, explained, "it’s not enough to sign up. You have to sign up and pay on a regular basis to really be enrolled."

That is one reason both state and private insurance officials have been saying their enrollments were shrinking.

"They've deteriorated quite a bit, this was anticipated to some degree, but I think it's exceeded expectations in some cases," said Jim Capretta of the Ethics and Public Policy Center.

For instance, state officials in Florida say their enrollments are now 220,000 lower than the administration's count in April, going from some 983,000 to just over 762,000, a drop of more than 20 percent.

A state official said some may have been duplicate enrollments because of website problems on Healthcare.gov. The others, he said, just didn't pay their premiums and lost their coverage, a problem insurance companies are also reporting.

Robert Laszewski, of Health Policy and Strategy Associates, said, "I've talked to a number of insurance companies around the industry and they're indicating that they're down as low as 70 percent of the original enrollments they had."

In fact, Mark Bertolini, the CEO of Aetna, the nation's third largest insurer, said recently that his company had 720,000 people sign up for exchange coverage as of May 20, but only 600,000 turned out to be paying customers.

He added he expects that number to fall to "just over 500,000" by the end of the year. That would leave Aetna's paid enrollment down some 30 percent from its original sign-up numbers.

Many analysts think enrollments across the industry will continue to erode.

"So the enrollment that the administration was touting in March and April," Capretta said, "I think you could bring that down by at least 20 percent going into the end of the year."

The Congressional Budget Office is predicting 13 million total enrollments at the end of the next open enrollment in February 2015. So the number they're starting from makes a big difference:

"If we've got closer to 6 million enrolled," Laszewski said, "they'd have to enroll more people in 2015 than they did this past year."