Ubuntu – How to view the complete changelog for a PPA package

The way to go is to upload once for every Ubuntu version.

Launchpad won't build packages for Ubuntu versions that are no longer supported, and only build a package for one specific version of Ubuntu. The targeted version is (as you already know) specified in the changelog file, by the newest entry!

Remember to be aware that the packages your program depends on might not be available at the same version across all versions of Ubuntu.

You also talk about "multi-architecture" (architecture = CUP type, eg. x86, LPIA, AMD64) this makes no difference since every package uploaded is build for all available architectures as long as you have Architecture: any in the package definition (debian/control) file, this also allows you to make the package depend on different packages for different architectures (be defining the package more than once)

In this context, the distribution field is irrelevant. Look in the official Ubuntu archives. Of course, you'll see that the top changelog entry will have "unstable" as the distribution for many packages. Likewise, all uploads that make it into the updates repository are actually copied over from the proposed repository. So a package in maverick-updates will actually say maverick-proposed in the changelog.

The importance of the distribution field depends on the tools that make use of it. For instance, if you use dput to upload to your PPA with: ~<your_launchpad_id>/<ppa_name>/ubuntu/ the distribution field in the changelog determines for which release the package will be built. But even this can be over-ridden by uploading directly to release you want with:

~<lp_name>/ppa/ubuntu/<ubuntu_release>

Launchpad's build from branch service uses the ability to copy a package from one PPA series to another. It doesn't actually care what is in the changelog for this. So the way you are currently doing things is correct.