As i've said several times in the past - my wife is a construction administrator for a very large building company in queensland. The construction they do undergoes several 'certification' or 'approval' steps, which include among others: approval for the development
approval for the plumbing sewerage plans
gasfitter's certification
'final' approval which is an inspection done by the council to confirm that all the conditions of the construction have been adhered to
Theres a bunch of others, and i've probably gotten the names wrong, but you can get approval to build, and then get the 'building' signed off, but that doesn't mean the gas fittings were signed off. The relevant authorities would sign off that the construction was completed as per the DA, but the gas supply cannot be enabled until the authorised gas fitter has certified the work. Think caravans - you can build a caravan from scratch, and get it registered by the department of transport (it's nothing but a trailer at the end of the day) - but the gas fittings installed need to be certified by a gas fitter separate to the registration... and you can't use the gas stove until that's done... make sense?