KC,
You seem to be creating much angst for yourself. Pigs are like people, they don't grow to formulas or charts, these are at best guides or rules of thumb to get you into the right area.
It is just like if you fed two children the same food, they will grow at different rates, and a lazier one might put on more fat than its brother who runs around and plays.
And you can't say that different breeds grow at different rates except at a population level. This would be like saying EVERY American is fat, Americans are at a population level larger than Europeans, but there are plenty of American individuals who are not fat, just as there are plenty of fat Europeans.
As pigs grow they will have times when they put on growth and times when they consolidate. These are not the same times for every pig.
The only way to get closer to uniform growth is to have a temperature and humidity controlled indoor environment, buy highly specialised hybrid pigs that are scientifically and selectively bred to be as like each other as possible, to not allow the pigs room to move much, feed different formulations almost every week of their life, feed lots of antibiotics to ensure no health issues, and even then you have pen with lost of variation within a range, but a good average weight over lots of pens to meet market conditions.
You have free range rare breed pigs designed to cope with lots of variation in both environment and feed– chill and enjoy them growing as nature intended !