Got it working.
I logged onto https://maven.java.net/index.html#welcome and deleted various staging repositories. Then I edited my pom so that version said
<version>2.0.4-SNAPSHOT</version>
rather than
<version>2.0.4</version>
and reran
mvn deploy -Dgpg.passphrase=xxxx
Now its available at
https://maven.java.net/content/repositories/snapshots/net/jthink/jaudiotagger/2.0.4-SNAPSHOT/
So now Im going to try and do a proper release, I assume I set version back to
<version>2.0.4</version>
but I cant find anything in the documentation that tells me I should do this.