Version control/Bug tracking at Rising Sun Pictures

You may have seen it because it's a famous slide but I'll link to it anyway.
"Adelaide University takes on the Earth" blog entry

Each movie might be running a different version of each piece of software

How they do it? I'm interested in its detail.
The only way I know is using an interface name (soname in this post).
but in a production it is not always good to fix a bug whenever you have find it, since what is the most important is sometimes to open a file later and see exactly the same scene as the one when it was created including bug behaviors, but it is troublesome to have artists update a software manually when you find a bug in it. It's a contradiction. Maybe a 3d software uses the latest software (plug-in etc.) automatically, but once a scene ihas been created, it keeps using the same version of the softwares? but how?