Now, to the uninformed Monk like myself, these plain-English explanations are not so plain. The latter refers to the former, strengthening the impression that these two settings do just the same thing. Is this some configuration cruft? or is there really some difference in how they behave?

They are certainly not the same. The directories you give to otherlibdirs will be added to @INC, unconditionally. The directories you give to inc_version_list will be inspected to see if it contains one or more directory trees that could be a set of Perl modules. Directories found this way will be added to @INC.

This text is showing the results or effects of configure-time choices, not the choices themselves.

That's because it's the effect of not using configuration options. It does say (if you don't change the Configure defaults) after all.

For more than 99.99% of the cases, there's no need to fiddle with with the options mentioned. Given a normal previous install, and the installation of the new version in the same place, Configure will do the right thing.

Abigail