7.3. Version Strings

SystemImager releases use an X.Y.Z numbering scheme similar to that used by the Linux kernel. X is a major feature release revision incremented to show significant architecture changes. Y is a minor release revision, incremented to show the addition of new features. Z is a bug-fix revision. If Y is an odd number, the release is a development release. If Y is even, it is a stable release.

Using this scheme, you can see that 2.1.3 is a development release because 1 is odd. You can assume that the only changes between 2.0.3 and 2.0.4 were bug fixes, because only the last digit was incremented.