What is the most significant practical difference between FICO 9 and FICO 8 in terms of credit scoring?

FICO 9 made two major changes that benefit consumers compared to FICO 8: paid collection accounts are completely ignored, and unpaid medical debt collections carry significantly less weight. Under FICO 8, a paid collection still drags down your score, but FICO 9 effectively removes that penalty once the debt is settled. Many mortgage lenders still use older FICO versions, so consumers may see different scores depending on which model a creditor uses.