Higher income with lower assets could explain the difference. Or # of kids, # in college, medical bills, debt…any number of things. (I just filled out the Profile and was surprised it did ask for credit card, auto loans and other consumer debt amount - so that may be school-by-school, or year by year as I don’t recall seeing it before).
Pretty much the only negotiation UPenn does is if financial circumstances changed - they might offer more if a parent is suddenly unemployed or someone dies or a $25K medical bill hit the family after the FA app. And if another ivy offers a better package they may match (Cornell does that, not sure about Penn).
Beyond that, the NPC is what will tell YOU how much YOUR FAMILY will be expected to pay.