I just downloaded several example projects, each of which have an open-source class that I was after, and you are supposed to copy the class into your own project.
However there is no indication at all which is the newest version of the class.
Maybe people could just add a note with the SQL date when they add a class to their project?
I know I will do now (even for my own use).
It might also be useful for the class authors to add a Private Constant or a note to their classes indicating the version # of the class itself.
I requested such a Version Constant from chargeable PlugIn Devs too. Such a constant helps in many cases. 
i do it with all my internal classes/modules that way I know when I am working with a newer or older version.
There are a few simple things that I’ve been doing to keep my code organized. For example, I’ve been adding version constants to classes and modules, and a few notes as well.
The notes include an overview of the class, who developed it, its history, and in most cases, a few examples of how to use it. If it’s a class that I’m making available to other developers, I also include the open source or commercial license. And if it’s a class / module that needs work done to it, I often keep a To Do / Wish List note as well.
Here’s a screenshot of what the latest Aloe module looks like, showing some of those constants and notes.
I also keep a list of the modules and classes that I reuse, along with the latest version info, and what project they can be found in. That way, when I open up a project that I haven’t worked on recently, I can see what is out of date and where to go to get the latest versions. It’s not ideal, but it works.
For version numbering, I follow the semantic versioning suggestion http://semver.org/ but whatever works for you works
You may need to ask each author to add such notes or constants individually.