More than 11 million people signed up for private health insurance under the Affordable Care Act during the 2015 open enrollment period that ended Feb. 15, the Obama administration announced Tuesday. But the numbers are just preliminary and, depending on several factors, could fall or rise further.

The number could grow because the government has extended the deadline until Sunday, Feb. 22, for those who had technical problems signing up over the weekend or had to deal with long wait times when signing up through the ACA’s call center. (More people signed up on Sunday, Feb. 15, than any day during the 2014 and 2015 enrollment periods.) The administration also is considering adding a special enrollment period around the time when taxes are due in April and when people realize they will have to pay penalties for not having health insurance. Many of the states that run their own exchanges have also extended their deadlines.

But the number could fall. In 2014, 8 million people signed up during the first open enrollment period of Obamacare, which ended in April of that year. But by the time fall came around, 1.3 million people had dropped out of plans run by the exchange, although some may have found coverage elsewhere. Forbes then calculated that plans offered on the exchange had a retention rate of 87 percent.

The 11.4 million figure that's touted by the government also doesn’t necessarily reflect the number of new enrollees. Forbes reported that of those who signed up for coverage during the 2015 open enrollment period, about 5.4 million new enrollees had been previously uninsured -- less than half of the 11.4 million enrollees -- meaning that the rate of new enrollment in health care plans had slowed significantly. Estimates from last year put the number of uninsured people gaining coverage through the Affordable Care Act exchanges at 10 million, or almost twice as many as in 2015.

The other issue is that despite people signing up for health care, there's no guarantee they will actually gain that coverage, because they have to pay their premiums in order to actually be covered. About 80 percent of those who buy coverage through exchanges received government subsidies that covered about three-quarters of the price of monthly premiums.

The Congressional Budget Office has estimated that this year the Affordable Care Act reduced the number of uninsured Americans by 19 million. It also estimated that in 2015, 12 million people will get coverage through the exchange, a slightly higher estimate than the 11.4 million signed up so far, and nearly 3 million more than the White House’s initial projection of 9.1 million sign-ups for the 2015 open enrollment period.