In April 2011, Dan is audited by the IRS for the year 2009. During the course of the audit, the agent discovers that Dan's deductions for business travel and entertainment are unsubstantiated, and a $6,000 deficiency assessment is proposed for the tax year 2009. The agent also examined some prior-year returns. The agent discovers that Dan failed to report $40,000 of gross business income on his 2007 return. Gross income of $60,000 was reported in 2007. The agent also discovers that Dan failed to file a tax return in 2002. Will the statute of limitations prevent the IRS from issuing a deficiency assessment for 2009, 2007, or 2002? Explain.