When we designate a version with an 'x', such as NEMS Linux 1.2.x, we mean anything within the 1.2 rolling release cycle. This means 1.2 (which can also be considered 1.2.0 if desired), 1.2.1, 1.2.2, and so-on.
A rolling release is a second decimal point release, and rolling upgrades are available within each major release as made available. Rolling releases are usually pushed out in order to fix bugs or improve features. An example of a rolling release would be going from NEMS Linux 1.2 to 1.2.1, or 1.2.1 to 1.2.3. Once a new NEMS Linux major release is available, it is recommended to perform a major release upgrade to ensure you have the latest and greatest NEMS Linux has to offer.
These steps may be followed to upgrade from one major point release to the next major point release. For example, this process will take you from NEMS Linux 1.1 to NEMS Linux 1.2, or NEMS Linux 1.2.x to NEMS Linux 1.3, or ultimately, NEMS Linux 1.3 to 2.0, and so-on.
See legacy upgrade documentation here: http://www.baldnerd.com/nems-migrator-legacy-upgrade/