As mentioned in dpkg-source.1, section “Format: 3.0 (quilt)”, source
packages with format 3.0 (quilt) support additional component tarballs
alongside the main tarball.

dpkg-source-gitarchive currently seems to ignore such tarballs when
building source packages.

3.0 (quilt) seems to include all tarballs that match
<package>_<version>.orig-<component>.tar.<ext> as components. So I
think the most sensible behavior for 3.0 (gitarchive) would be to
include all such matching tarballs found in pristine-lfs.

Regards
Sven