I ended up in a situation where Google Earth updated, and the new version does not work. I wanted to revert back to the just prior version, and I discovered I had not made a copy of the prior version's package file. Browsing Google's APT server greeted me with many unhelpful 404 pages... browsing the APT server discouraged!

So there is a standard to how the repositories are laid out. Knowing certain things allows by substitution to correctly arrive at, in this case, other versions of packages that should be also on the APT server.

I began by examining the sources.list file for Google Earth, and comparing it to another repository I also have added. The one for Google Earth is as follows:

So from that, and comparing to another, I now know that I should be able to traverse:

to obtain the list of packages in the repository. File download instead of a 404 page. The /dists/ directory is injected statically to what is listed in the APT sources file, and then the APT compatible tools tack on a static /binary-amd64/Packages to obtain the list of packages on the APT server.

I will only paste in the one entry of interest to me in that file.

That "Filename:" keyword... that is the one! So also on APT repository servers is the pool directory where the packages are stored.

The pool directory location is also based on the entry in the APT sources file.

So combining details leanred from the APT sources file / the list of software currently listed as in the APT catalog / combined with the version of the sought after just prior version, I arrived at the following working URL:

Bingo!!! That downloads the sought after version of the package to successfully roll back my system.