BlackBerry 10 files are given version numbers in the format 10.x.y.zzzz. We will explain what these mean.
The OS version always starts with 10, and will start with 10 for the foreseeable future.
Minor revision. Generally 0 in the case of 10.1 and 10.2 releases (except for 10.2.1, which is in early development), but 10.0 releases incremented this through the pre-release phase and shortly afterwards. The highest minor revision for 10.0 is 10.0.10.
Version. Usually, higher numbers mean that an OS is newer than its predecessors, although some of the later 10.1 releases didn't follow this rule. 10.1.0.2420 has a build date of Jun 03 2013 19:29:38, whereas 10.1.0.2074 has a build date of Jun 05 2013 11:39:56. It can be seen that 10.1 development branched into two parts; from 10.1.0.2342 to 10.1.0.2420 for Europe, and 10.1.0.2025 to 10.1.0.2151 for North America.
Radio and SDKEdit
For a given OS, there also exists a radio and SDK version. The radio is what allows the device to connect to networks, and the SDK is a stripped-down version of the OS for developer usage. SDKs are released infrequently. The radio version is OS version+1, and the SDK version is OS version+2.
As an example, 10.1.0.1483 is an OS, 10.1.0.1484 is a radio file and 10.1.0.1485 is a SDK. This means that the next OS after 10.1.0.1483 would be the hypothetical 10.1.0.1486, with a 10.1.0.1487 radio and 10.1.0.1488 SDK.
BlackBerry 10 OS releases sometimes have a software release in addition to the version number. If your device returns a software version, then that means your carrier has the operating system in either testing or deployment. If you don't have a software release, it's not important.