Michigan: ACA Medicaid expansion reaches up to 15% more than supposedly eligible??

I've written about this many times before, and now it's just gotten surreal. Depending on your source, Michigan supposedly has somewhere between 477,000 - 500,000 residents eligible for ACA Medicaid expansion...but they passed the lower end of that range months ago, the upper end several weeks ago, and as of yesterday, reported that a whopping 547,000 people are now enrolled in the Healthy Michigan program:

Healthy Michigan Plan Enrollment Statistics

Beneficiaries with Healthy Michigan Plan Coverage: 546,807
(Includes beneficiaries enrolled in health plans and beneficiaries not required to enroll in a health plan.)

*Statistics as of February 9, 2015 
*Updated every Monday at 3 p.m.

Again, it's possible that the initial estimates were simply too low to begin with, or that the number of Michiganders eligible for the program has gone up by 30K or so since those estimates were made. Even so, we're quickly reaching the point where "we underestimated" isn't going to be enough to explain the discrepancy. Depending on which estimate you use, Healthy Michigan has now enrolled anywhere from 9-15% more people than are supposed to have been eligible for the program.