A new Avo version is released every four-ish weeks, usually on Tuesday. The versioning scheme does not follow semver but a series release.
The current series is series 3 (version 3.1, 3.2, 3.9, etc). Every second Tuesday of the month we'll increment the minor version number (from 3.7 to 3.8).
In-between that release cycle we might release patches (3.7.1 or 3.9.5) that address particular bugs or issues that are more urgent and can't wait for the next release cycle.
Sometimes we publish pre-releases (3.7.1.pre.1 or 3.5.2.pre.7).
The pre-releases are usually built on our machines and will be builds from a specific branch, so they don't follow any particular convention. The pre.2 might contain a fix, but the pre.3 might not contain that fix because they might be built from different branches. We usually mention on a PR or issue to the bug reporter if they should or shouldn't use pre-releases. They won't get installed in regular bundle update avo commands, unless you specify it in the Gemfile.