I completely agree, Lemon, that not every day is the same. It's one of the hardest things I've had to come to accept as the mom of a toddler: some days he just eats more than others.
When it comes to the number of feeds, Tracy recommended that the DF start to be phased out by ~8 months, or really, when LO was comfortably on 3 solids meals a day plus bottles/bfs. Just at some point, the calories should make the shift completely to daytime. But yes, there will be variations from the day to day in how much your LO eats...plus as they get away from so many milk/bottle feeds and make an even great leap towards eating like a toddler, the exact number of ounces won't be that big of a deal. At this age (and for a good while after), LOs are very capable of self-regulating, i.e. knowing when they're full/when to stop eating and when they're hungry.