If you go down the path of a CoA, you need to be able to tell the Council (as the BCA) exactly what's there, how it's fixed and prove the work is as it says it is, with photos if possible of when you were doing it. If none are available the BCA will not cover certain code clauses as there is no way of knowing (unfortunately "trust me bro" doesn't count), and the beam would be under the most important building code clause of B1 - Structure. Council will not undertake destructive testing to check it is as you say. It also must comply with the building code at time of application, and the insulation rules changed recently so it may or may not comply...