Maybe I am wrong, but it think in the upstream tarball (gnome-themes-2.20.0.tar.gz) includes all themes and they would be installed to DATADIR/themes/. The decision which theme belongs to which package seems to be done only in the debian/gnome-themes*.install files in the source package.
Maybe I am wrong, but it think in the upstream tarball (gnome- themes- 2.20.0. tar.gz) includes all themes and they would be installed to DATADIR/themes/. The decision which theme belongs to which package seems to be done only in the debian/ gnome-themes* .install files in the source package.