To my understanding:

Half full fishtank on scale. Scale reads 10 pounds. 1 pound boat is placed in tank, water level rises, tank does not overflow. Scale reads 11 Pounds.

Same scenario except with neutrally buoyant 1 pound submarine. Same results.

Same 2 scenarios, except all displaced water overflows. Scale still reads 10 pounds.

Empty container on scale. Scale reads 1 pound. Neutral buoyancy hydrogen balloon weighing 1 ounce floats inside. Scale reads 1 pound.

6 ounce hummingbird rests on perch inside 1 pound container on scale. Scale reads 1 pound, 6 ounces. Hummingbird takes flight and hovers. Scale still reads 1 pound 6 ounces when you average any fluctuations. I find this one a little hard to swallow, but it seems to be the popular opinion here.

I understand all these to be true then. Am I correct?