Interesting. Mine was MI01 as well last time I looked. It's now MI03. Not sure if it really means anything, but we'll know soon enough. I hope to take delivery of mine this week (prod start April 18th).
Hmm, mine did not change (delivery on may, 11th). However, I am now able to change MI01 into MI03 in the design-view URL. that didn't work a few weeks ago (returned empty response), now it generates a PDF that is identical to MI01.
So whatever the change is, it doesn't look like it has anything to do with a changed design somewhere.