Joint credit card accounts mean both account holders share a single combined credit score for that account. True or false?

Joint credit accounts are reported to the credit bureaus for both account holders, and each person's individual credit score is then calculated using their own full credit history — including that shared account. There is no such thing as a combined or shared credit score. If the joint account has a late payment, that delinquency appears on both individuals' reports and affects both of their scores independently. This is why it is important to only open joint accounts with someone whose financial habits you completely trust.