There are a lot of people (including myself, unfortunately) who would be able to get along well on much less than 2,000 calories per day for an extended period of time, if need be.
True. The 2,000 calorie day is still a useful unit for counting how much food you have. I could go on short rations if necessary, but I don't think I would take my family down that road in the first 30 days of an TEOTWAWKI event. I'd rather be at full strength and maximum energy until things stabilize. After that, losing 5-10 pounds of body weight and conserving rations for the first year sounds like a good plan. If you eat less and prefer 1,500 or 1,200 calories per day for figuring, that makes sense too.