LAST_TAG not working

Hi,

i might be using it wrong but i want to see all changes between current build and last build that has a tag (any tag?), and if i understand correctly the "LAST_TAG" is according to the jenkins builds tags, not the git tags?

using the syntax below still only gives me changes since last build, not since the last tag. am i using it wrong?
thanks
Asher

using:
def publisher = LastChanges.getLastChangesPublisher "LAST_TAG", "SIDE", "LINE", true, true, "", "", "", "", ""
publisher.publishLastChanges()
def changes = publisher.getLastChanges()
println(changes.getEscapedDiff())
for (commit in changes.getCommits()) {
println(commit)
def commitInfo = commit.getCommitInfo()
println(commitInfo)
println(commitInfo.getCommitMessage())
println(commit.getChanges())
}