All reports of version-substvar-for-external-package for the archive. The extended description of this tag is:
The first package has a relation on the second package using a dpkg-control substitution variable to generate the versioned part of the relation. However the second package is not built from this source package. Usually this means there is a mistake or typo in the package name in this dependency.
This tag has not been emitted in any package tested by Lintian.