The tag is present in Lintian version 2.109.3. That is the most recent version we know about.
The version number of this package contains ".dfsg", probably in a form like "1.2.dfsg1". There is a subtle sorting problem with this version method: 1.2.dfsg1 is considered a later version than 1.2.1. If upstream adds another level to its versioning, finding a good version number for the next upstream release will be awkward.
Upstream may never do this, in which case this isn't a problem, but it's normally better to use "+dfsg" instead (such as "1.2+dfsg1"). "+" sorts before ".", so 1.2 < 1.2+dfsg1 < 1.2.1 as normally desired.