Enrollment in exchange coverage increased from 6.3 million at the end of 2014 to about 8.8 million, according to figures released by the administration at the end of last week.

But Obamacare’s coverage gains have also been more modest than expected, particularly when it comes to the exchanges. And part of the problem seems to be that people who sign up for coverage at the beginning of the year don’t always follow through to keep their coverage effective at the end of the year. It’s a problem that seems to be larger than the administration knew.

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