All packages in Tribblix are versioned. If you look at the pages on the package repository you can see the current version of each package in the repo. On an installed system the pkginfo -x command will give you the package description and version.
As Tribblix is created from different sources, the meaning of the package version can vary.
For illumos packages, the version string matches the Tribblix release. For example, "0.18.0" indicate the Milestone 18 (0m18) release.
For packages inherited from another distro, the version matches in some way the distro release I got the packages from. For example, the OpenIndiana packages were (at this time) cut from the oi151a9 release, and have a version string "0.9o".
For packages I build directly from source, the version string is usually the upstream version, with a build number appended. Initially the build number is 0, then increments. If the upstream version is updated, the build number goes back to zero. So it's reasonably obvious what version of a package is installed.
For example, abiword is version 2.8.6 so the first time it was built the package version was 188.8.131.52. Over time the package has needed to be rebuilt, so it's now up to version 184.108.40.206.
The sharp-eyed will notice that the illumos packages have a build number in them. This hasn't yet been used, it's there just in case.
The scheme is reasonably flexible. For example, OpenSSL has letters in its releases - like 1.0.2j - which I could keep verbatim, but in practice I convert the letter to a numeric sub-version, hence 220.127.116.11.
There are some packages for which I originally forgot to add the build number. That OpenSSL package is an example, but there are others. I've tended not to correct those as it disturbs the flow, I will if it ever becomes convenient.
Some releases have a date, this is just converted to numerical form.
One thing that should be obvious is that the scheme doesn't guarantee that package versions are numeric. They're just strings; it just happens that most packages have version numbers that are numeric or can easily be represented as such.
Also, package versions don't necessarily increase, there is no sense of ordering built into versioning. For example (this does happen) there's an upstream version 1.2, which leads to package versions 1.2.0, 1.2.1, 1.2.2, etc. Then there's an upstream 1.2.1, which is packaged as version 18.104.22.168, which is lower than 1.2.2. And sometimes upstreams try a major version bump, then backtrack.
However, package management in Tribblix ascribes no meaning to the version numbers. It's only test for currency is this - does the version installed match the version in the repository catalog? If they're the same, then you're up to date. If not, then apply the version from the repo.
This then makes it easy to roll back errant packages. All I have to do is put the old version back in the catalog. Anyone who has applied the broken version will get a version mismatch and the older version will get installed whenever they update.
(This simplistic approach only works if I haven't built anything against the newer version of the package I want to roll back. But then, all I have to do is roll all those dependent packages back as well.)
Life's a little more complicated if you might want multiple versions of an application installed. In that case you have to have different packages. For example, I have separate packages for Python 2.7 and 3.6, and there might be 2 corresponding packages for any modules. I used to use multiple packages more extensively, sometimes even for minor version updates, but tend to avoid that now when I can.