If I have an account that is scheduled to come off my credit report September of 2010. Does that mean the last payment was made September of 2003?
It usually means that in September 2003, you first became delinquent, and never caught up. It is not a definitive date though if you are asking for court purposes.
Whatever you can prove in court. Do you have any account statements from the time in question? I'd start in September 2003 and work forward a year, and/or check around any time you think you may have made a payment.
The rule for a negative falling off the credit report is 7 years and is generally calculated beginning 180 days after the delinquency. The DOFD, while related, does not have legal implications for the calculation of the running of the statute of limitations.