BS stands for British Standards: it's not ONE standard as it covers all kind of stuff! The same for EN, which stands for European Standards. In this case it's more complicated as in Europe there is "Harmonization" of Standards.
ASME is form Mechanicals, and also you could find some...
I don't know exactly why the globe and ball valve should be kept in the position (opening) you said, but gate valve should be, always, in fully open or closed position, as any partially open opsition will increase the speed throught the valve and damage the disc and the seat, not allowing it to...