The first open-enrollment period under the Affordable Care Act ended this week with roughly 7.5 million people obtaining policies through the new state insurance exchanges. That’s an amazing and welcome result, considering how badly many of the exchanges stumbled when sign-ups began in October. Nevertheless, it’s far too early to judge the success or failure of the health care law, given that key tests of the program’s sustainability have yet to be passed.

Almost all of the exchanges got off to a wretched start, particularly the federally managed ones that shared a mind-bogglingly dysfunctional website. And yet, sign-ups increased dramatically as the deadline for enrolling approached.

It’s hard to say how much headway the law is making toward insuring the uninsured, however. The exchanges didn’t measure how many of their new enrollees had previously lacked coverage, as opposed to the number who signed up because their old policies had been canceled or because they were no longer covered at work. Although two recent surveys show a sharp drop in the overall percentage of uninsured Americans, analysts at Rand Corp. say most of the increase came from people gaining coverage through an employer, not the exchanges. And the refusal of about half of the states to expand their Medicaid programs has left millions of poor American adults unable to afford coverage.

Nor do we know yet whether the exchanges’ customers will find their new plans adequate. Many of those who signed up have yet to seek treatment from their new plans’ more restricted (or “narrow”) networks of providers, one of the key cost-saving steps insurers took in Year One. Another outstanding question is what will happen to premiums at the exchanges, which will depend to a great degree on the demand for health care from the new enrollees.