“I feel a huge sense of relief,” said Katie R. Norvell, 33, a music therapist in St. Louis, who has been uninsured for three and a half years and has a pre-existing gynecological condition, endometriosis. She signed up Dec. 22 for a midlevel silver plan offered by Coventry Health Care, owned by Aetna, and has already begun making doctor’s appointments.

“With coverage,” she said, “I can be my best self. Health insurance won’t control my job choices.”

A series of last-minute changes in rules and deadlines for people to sign up and pay premiums have left less time for insurers to activate coverage and issue identification cards, adding to the uncertainty caused by the troubled rollout of the health exchange.

“There will be a lot of confusion,” said Brian D. Caswell, a former president of the Kansas Pharmacists Association, who owns a drugstore in rural Baxter Springs. “Many people will get insurance cards, but will not have a clue what’s covered, what’s not covered and what they are supposed to pay.”

Others may find their insurance companies have no record of their enrollment because the information was not sent by the online marketplaces where they signed up for coverage. Some of the newly insured may have trouble finding doctors who accept their health plans, many of which are restricting the number of providers in their networks to hold down premium costs.

And as newly insured consumers sort through details of their coverage, others will find that they are no longer insured by their old plans, which were canceled or discontinued because they did not comply with coverage requirements of the law. Of several million who received cancellation notices, most should be able to obtain other coverage, the Obama administration says.