Distinction between a/b versions of Matlab?

Solution 1:

MathWorks has been putting out two releases of MATLAB per year for the past few years. The first one early in the year is a and the second one later on is b. The b release is a new version of MATLAB, not an incremental update.

They started this versioning scheme in 2006 and still maintain a numerical version number in the background. Here's a release history.