If every detail of the half-staff rules were to be followed, it seems to me that the US Flag could be at half-mast for the majority of the year. There's (I think) 6 former US Presidents still alive. Presidents Carter, Ford and Reagan are getting up on years. If they all happened to pass in the same year, that's 3 months of half-mast gone. Half the Senate is over 65- all very good candidates for heart attacks or some other form of passing... accidents, assassination (what with terrorist attacks going on- and possibly coming again). I'm not sure how many ex-vice-presidents we still have left, but it's probably somewhere in the same ball-park as our living presidents- so there's another potential month gone.
President Eisenhower, leader though be may have been, should have checked his math. His executive order was a good idea in theory, I think, but it might have fallen short of practicality. I mean, if we get attacked again at the wrong time and at the wrong place, we could easily end up with our US Flag at half-mast for more than 6 months.