All reports of copyright-should-refer-to-common-license-file-for-gfdl for the archive. The extended description of this tag is:
The strings "GNU Free Documentation License" or "GFDL" appear in the copyright file for this package, but the copyright file does not reference /usr/share/common-licenses as the location of the GFDL on Debian systems.
If the package uses some other license that just mentions the GFDL and that Lintian should detect as an exception, please file a Lintian bug. If the copyright file must mention the GFDL for reasons other than stating the license of the package, please add a Lintian override.
Refer to Debian Policy Manual section 12.5 (Copyright information) for details.
This tag has not been emitted in any package tested by Lintian.