A caveat right off the bat: RAND’s estimate only runs through March 28 whereas the actual deadline for signing up was March 31st. Given the crush of traffic on Healthcare.gov in late March, many more people could have signed up over those last three days than were captured by these numbers. On the other hand, the White House was claiming six million sign-ups as of March 27. There’s no way to reconcile that with RAND’s data.

One of them is wrong. Maybe both, in fact.

There’s a big spike in Medicaid, just as everyone expected. There’s a less big but still seven-digit drop in coverage on the individual market, as people discovered that if you like your plan, you might not be able to keep it. There’s not quite four million sign-ups on the new ObamaCare exchanges, not seven million and change like Obama insisted in the Rose Garden. And then there’s that eye-popping “ESI” category. That’s “employer-sponsored insurance,” the sort of coverage that 100 million people already have through their jobs. Er, why would eight million people have suddenly gained that type of coverage last year when the U.S. labor force assuredly didn’t expand by eight million? Good question. Says RAND:

Some of these newly insured individuals may have taken up an employer plan as a result of the incentive created by the individual mandate; others may have newly found a job. The U.S. unemployment rate fell slightly between September 2013 and March 2014, so part of the increase in ESI enrollment could have been due to economic recovery rather than the ACA. While the 8.2-million-person increase seems large, more than 100 million 18- to 64-year-olds were covered by ESI in 2013. Since ESI is the dominant source of insurance coverage among this age group, it is not surprising that we could see relatively large effects of the individual mandate and economic recovery in this category.

Yeah, but 8.2 million people? That seems implausibly high, and not just to me. Maybe there’s a giant class of young adults out there who are employed but who have been declining coverage through work because they didn’t want to take a hit on their paycheck. Once the mandate went into effect in October, they decided that they had no choice and set about trying to decide if their work plan or a new exchange plan would be better. Surprise: The work plan’s better. Or cheaper, at least.

One other tidbit via health-care wonk Adrianna McIntyre:

Money shot from the new RAND study. Estimated 36% of exchange enrollees previously uninsured (before March surge): pic.twitter.com/e9GpE8jToX

— Adrianna McIntyre (@onceuponA) April 8, 2014

Another way to look at that is that, of the five ways that uninsured people could have changed their status this year, the ObamaCare exchanges ranked fourth. ESI and Medicaid both drew more uninsured than the exchanges did; the mandate, quite naturally, is driving most of the uninsured into less expensive options. In fact, per that table, there are actually more people who had insurance through work last year and now have no insurance at all (2.1 million) than there are people who had no insurance last year and now have it through the exchanges (1.4 million). Something to watch going forward.