Once in a lifetime event is a meaningless statement(who's lifetime? How long is that exactly?).of course taken literally then If 3 happened in a week then none could be a once in a lifetime event. I think your confusing it with a once in a 100 year event which has quite well defined statistical meaning. Oh and just because one of those events happened last year doesn't mean we won't or even shouldn't see one this year or for another 99 years even.
