You need to retain these tarballs in the parent directory for dgit
build and dgit push.
+dgit repositories could be cloned with standard (git) methods. The
+only exception is that for sourcefull builds / uploads the orig
+tarball(s) need to be present in the parent directory.
+
To a user looking at the archive, changes pushed using dgit look like
changes made in an NMU: in a `3.0 (quilt)' package the delta from the
previous upload is recorded in a new patch constructed by dpkg-source.