INDIANAPOLIS (AP) — Record-keeping snags could complicate the start of insurance coverage this month as millions of people begin using policies they purchased under President Barack Obama's health care overhaul.

Insurance companies are still trying to sort out cases of so-called health insurance orphans, customers for whom the government has a record that they enrolled, but the insurer does not. They are worried the process will grow more cumbersome as they deal with the flood of new customers who signed up in December as enrollment deadlines neared.

The government says the problem is real but under control. Officials say the total number of problem cases they are trying to resolve with insurers currently stands at about 13,000. That includes orphan records. More than 1 million people have signed up through the federal insurance market that serves 36 states. Officials contend the error rate for new signups is close to zero.

Insurers, however, are less enthusiastic about the pace of the fixes. The companies also are seeing cases in which the government has assigned the same identification number to more than one person, as well as so-called "ghost" files in which the insurer has an enrollment record but the government does not.

But orphaned files — when the insurer has no record of enrollment — are particularly concerning because the companies have no automated way to identify the presumed policyholder. They say they have to manually compare the lists of enrollees the government sends them with their own records because the government never built an automated system that would do the work much faster.

"It's an ongoing concern," said Robert Zirkelbach, a spokesman for the industry trade group America's Health Insurance Plans. "Health plans can't process enrollments they haven't received from the exchange."

Julie Bataille, communications director for the federal health care rollout, disputes the industry's view.

"We have fixed the issues that we knew were a problem, and we are now seeing nearly zero errors in the work moving forward," she said.

A federal "reconciliation" team, including technicians, deals directly with more than 300 insurers to resolve signup problems, she said, while the government's call center has caseworkers to help consumers directly.

Insurers use the term "orphan" for the problematic files because they are referring to customers who have yet to find a home with the carrier they selected. The files have cropped up since enrollment began last fall through HealthCare.gov. The site was down an estimated 60 percent of the time in October.

Since then, the front-end interaction between customers and the website has largely been fixed.

But insurers worry that the back-end problems will grow more acute as they process the wave of customers who signed up at the end of 2013. More than 2 million people had enrolled by the end of the year, either through HealthCare.gov or state-run websites.

Aetna spokeswoman Susan Millerick said orphaned files were "manageable over the short term." But she added that manually comparing enrollment files will not work over the long term and that the federal website needs a permanent fix to eliminate the possibility of orphaned files.

Bataille said the administration is working the issue with every tool at its disposal, from software fixes to picking up the phone and calling insurers.

Among those who got lost in the paperwork confusion was cancer survivor Sharon Van Daele of Tucson, Ariz., who went back and forth between her insurer and the federal government for more than a week after her confirmation failed to arrive. Unable to get answers, she said it felt as if she had fallen into a black hole.

She started the year worried she was uninsured even though the HealthCare.gov website told her on Dec. 22 that she had successfully enrolled.

"I made all the deadlines, and then I tried to make my payment, but they wouldn't take it," said Van Daele.

Her case was finally resolved after an official from the federal Centers for Medicare and Medicaid Services contacted Van Daele directly, following an Associated Press inquiry to the agency's Washington press office.

Van Daele is in remission following treatment for a type of blood cancer. Her previous coverage lapsed Dec. 31, and she started getting nervous when nothing for her new coverage arrived in the mail.

"My husband told me I shouldn't leave the house," she said.

Insurance industry consultant Bob Laszewski said he expects to hear more reports about orphaned files as patients begin to seek health care or start worrying about insurance cards that have not arrived.

"As we go through the month, you bet this is going to be a problem," he said.

Improving weather also could turn up more orphaned enrollees. The year started with a blast of freezing weather that settled over much of the U.S. Those conditions usually keep people indoors and out of the health care system unless they absolutely have to use it.

Laszewski and other insurer representatives say orphaned files exist largely because the government allowed people to sign up without first guaranteeing the technology would work.

Insurers say it usually takes a few days for a customer's file to reach them after they enroll through the exchange. People who still do not receive their insurance cards and introductory packet after that should call insurers first for help.

If the insurer has no record of them, they must contact the government for help.