In a pure kinda way, it's almost a good thing that randomized events can happen more than once - i have yet to witness any double dose of Mega stuff but if & when the Jagged Knife cuts my planned strategy a whole 75% worth of delays it'd be really mind boggling to cope with a second wave of galactic scramblings.
Simulation or Deterministic gameplay can satisfy two type of players... the former being what similar or exactly the same Mega Events would do to wreck the latter's plan for an easier game or randomly made tougher by destiny instead of optional settings. Hence, selection of any variable Mega-Events set(s) at initialization would solve that & many other conditions.