The more mid cycle numbers you get, the better. It's the number that tells you how your dose is working. So, if we knew the nadir today was low, we'd know the pmps was a bounce. If the nadir was in the 300s, then we'd figure the whole cycle was probably flat. Because we don't know, we can err on the side of caution.
The bounce is hard to wrap your head around. When his body perceives a number that feels low, or lower than it is used to, it panics and releases extra glucose. That causes the number to bounce up because there is more glucose in the body than there would normally be. Some people call it Liver Training. The body has to get used to the lower ranges and then it will eventually stop releasing the glucose. Then the bounces stop.
The reason you look back at the previous cycles is because if a dose of X caused him to drop to Y last night, then you might get the same result tonight with X on a similar number. If X on a pink caused him to drop 70% yesterday, then you'd figure the X might be too much for a yellow tonight. You use your past data to guess how he might react.
Hope I haven't completely confused you.