I doubt they only store it for a month. Besides how cheap (in national security budget terms) it is to store everything indefinitely, the timespan of a month is

I doubt they only store it for a month. Besides how cheap (in national security budget terms) it is to store everything indefinitely, the timespan of a month is just not enough time to gather enough intelligence, especially when you don't know what you're looking for. If you're already capturing everything, you want a big picture, and a big picture isn't something you get with just what's been happening for the past month. If they ever delete stuff, it's based on tiers with different priorities (https://news.ycombinator.com/item?id=7394346 https://news.ycombinator.com/item?id=7394346), not an arbitrary period.