So they are going to run smaller than modern portions if people eat more now. Similar products should at least have similar serving mass, although there is room for adjustment for practical reasons like rounding to whole units. I’m not sure how new products without an early analogue are set.
I’m pretty sure they are standardized between product categories. I actually eat serving sizes, and most salty snack foods are 28g.
It seems like it’s based on portions recorded for the food type 40-50 years ago.
https://foodlabelmaker.com/regulatory-hub/fda/serving-size/ https://www.fda.gov/media/102587/download
So they are going to run smaller than modern portions if people eat more now. Similar products should at least have similar serving mass, although there is room for adjustment for practical reasons like rounding to whole units. I’m not sure how new products without an early analogue are set.