The right to remedy in the first instance is I am sure fairly entrenched in law.  If you were never given the opportunity to re-visit and if necessary put right then I do not believe you can be held culpable, unless the situation was immediately dangerous and you were unavailable, and even then I would have thought the onus was on them to prove they attempted to contact you.

To strengthen your case, do you need to file a complaint with the PGDB over uncertified gas work?  You obviously have proof that work was carried out by someone other than yourself in the court papers.  And for a certifier to do work and not certify it - well there really is no excuse is there.  I agree, and I drum in to my apprentices to keep good work diaries and to never throw them away, especially when it comes to gas work.

You can privately contact the Federation through Wal if you need any technical advice as we now have a small group who have made themselves available.