I do not know about the laws in Philly. In Kansas they passed a new law in July 2001. It states that no matter how long ago you got a DUI, it will remain on your record. Also if you ever get another DUI the once you already have had (even a diversion) will be counted in determining what offense your current DUI is.
For Example: A friend of mine got a DUI 22 years ago. now with the new law if he was to ever get another one he would be convicted of his 2nd.
I hope for your sake that this law is not the same in Philly, cause if it is you will be convicted of your 4th dui if you ever got another. I believe this is a felony and carries some very heavy penalties.
If you want to know the answer to your question you might want to just ask the prosecuting attorney (district attorney) in your town or region. I am sure they can help you.
Good luck to you.
Bini