In our products we use several dependencies. We need to keep track of our dependencies, their versions that we support/need, and the same information about their dependencies.
Currently we aim to support Python 2.4 and up, and might still do that for a while. Pootle and Virtaal depend on the Translate Toolkit, but we don't need to artificially ensure backwards compatibility, since anyone installing Pootle or Virtaal from outside their repositories, are likely to be willing to install the Toolkit as well. Our packagers tend to update these things together for the case of official distribution packages.
You might want to check the versions available in common distributions:
Sometimes it isn't trivial to find out when a certain package or distro was released, but Wikipedia articles are very useful: