Your question is very State-specific, that is it would depend on the law in your State and the policies of your prosecutor's office. The Statute of Limitations is shorter for a misdemeanor than a felony. Does your State make a 3rd DUI a felony? If so, the longer Statute of Limitation may apply. Is the only reason it has not been filed that you are taking the class? That would have to be answered by the prosecutor's office. You should consult a local criminal attorney who is versed in your State's laws and the policies of the prosecutor's office.