The tag is present in Lintian version 2.104.244. That is the most recent version we know about.
The given init script seems to refer to
using a file from there. Without a dependency on
Required-Start or Required-Stop, as appropriate, the init script might be
/var is mounted or after it's unmounted.
Using Should-Start or Should-Stop to declare the dependency is conceptually incorrect since the $local_fs facility is always available. Required-Start or Required-Stop should be used instead.
Refer to https://wiki.debian.org/LSBInitScripts for details.