ref the 20,000' max flap extension limitation.
Firstly, I'm not a DC-10 pilot but my type also has the same limit.
When I asked, I was told that they don't really think you'll ever NEED to put out flaps etc at anything like this height, never mind ABOVE it.
Therefore testing a/c behaviour at various flap settings is only done up to FL 200.
They could do it higher up, indeed as high as your a/c is certificated to, but why?
All costs money.
On my type there's no need, but maybe on the MD, they oughter
.