The khaki inners are pockets, of the type seen on other nationality BDs. It certainly looks like a correct lable in its original position, and not a converted service dress (I have an RAAF service dress cut down to BD style). I did think it might be a WAAF blouse but photos I have of RNZAF WAAFs show they also wear the usual closed collar.
Its more likely that its a wartime made item, that has been retailored later so it can be used post war, rather than be discarded just because of the change in style. As Chris mentions, the service number seems high for wartime so would also indicate post-war use. Wartime RAF uniforms with post-war badges are common, and in fact the only other RNZAF BD Ive had although still in wartime style and dated 1944, was post-war badged.