The orange layer between the 80 mm Anticon blanket and the top of the rafters is the foil backing on the insulation. Where it is taken up and over the roofing battens it looks like a separate material, but it's just the foil backing. The layer between the plasterboard and the rafter end is 15 mm plywood. Similarly, under the boxed eaves there are actually three layers of material - 4.5 mm fibre cement to protect the plasterboard, then the 16 mm plasterboard, then a layer of 15 mm plywood. As you say, the layer of 15 mm plywood is un-labelled, but is identified in the BAL-FZ diagram on p.

"Common studs" can be crippled (straightened) with a sawcut and cleats as per Fig. 6.2 of AS 1684.2. Crippling is limited to 20% of the studs in single or upper-storey loadbearing walls, ie. the "common studs". Studs supporting a concentration of load are a special case. These must not be crippled. Calculation of the input to determine sizes of studs supporting a concentration of load is explained in clause 6.3.2.2 and illustrated in Fig. 6.13.