systemd-delta
systemdPackage: systemd
Lists the unit files you have overridden or replaced, and how they differ from the package's. It answers "what was changed on this machine" without a trawl through /etc/systemd.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
systemd-delta --type- Filters by kind of divergence:
extendedfor drop-ins,overriddenfor full replacements. Plainsystemd-deltashows everything the machine changes relative to its packages.