The tag is present in Lintian version 2.104.244. That is the most recent version we know about.
dh_python3 has an override mechanism
debian/py3dist-overrides) that lets you specify different
prerequisites for particular Python
debian/py3dist-overrides is mainly used for Python programs
that use GObject introspection, since
dh_python3 cannot yet
detect that the packages
gir1.2-- map to Python imports,
so overrides are needed.
When the same import appears twice in the file, the information from the first one is used but all the others are discarded. That can lead to missing prerequisites.
An example of a second line that gets ignored:
gi.repository.Gst gir1.2-gst-plugins-base-1.0 gi.repository.Gst gir1.2-gstreamer-1.0
An example of a double dependency that gets kept:
gi.repository.Gst gir1.2-gst-plugins-base-1.0, gir1.2-gstreamer-1.0
Refer to Bug#980987 for details.