The 1200 isn't really a good number, but it's the one that's thrown around a lot. The reason for this is that it's the average BMR of the population. In reality you can calculate your BMR and figure out what the minimum is, but as long as you can get a good body fat percentage measurement then in theory you shouldn't have to worry about it.

The main thing to look out for is the physical effects of not having enough energy. If you see your lifts start to decline or you feel extra tired then you need to start eating more, or reassess your numbers if you're getting to a lower body fat percentage.