I'd need the whole question to comment on your concerns there.
However, so far as unusable fuel is concerned, that has always been included in the declared empty weight for the aircraft .. see CAO 100.7.2 definition of empty weight. ..
www.legislation.gov.au/Details/F2015L01127
Interestingly, empty weight used to include undrainable oil, to accommodate the often significant oil consumption of the larger radials ,, ie, oil was a consumable. Following a number of robust discussions (read arguments) back in the 70s between me and the then DCA engineering folk over my preference to include full oil in the empty weight for small aircraft, the Order definition was changed to the more sensible full oil configuration
It is worth keeping in mind that, depending on the particular aircraft fuel tank system configuration, a portion of the declared unusable fuel will/may be quite usable for normal attitudes in flight (but not available for flight planning). This is due to the way in which unusable is determined by flight test. The required tests simulate turbulence, generally by setting up a rock and roll motion with small rudder inputs. Unusable is when the engine being fed hiccups. The actual quantity is determined by switching to another tank, landing, and draining the test tank.
