Quoting Markus Koschany <apo@debian.org>:
Why don't we add all DFSG-free licenses to /usr/share/common-licenses or /usr/share/free-licenses instead? It would save a lot of developer and maintenance time
...
IMHO using links and references is just common sense and reduces unnecessary make work.
+1 with "all DFSG-free licenses" == \ "all DFSG-free licenses used by at least 0x10 packages".