The best place to check for this kind of information is DMV. It's possible that, because your DUI is so old, it has fallen off of their radar and you might need not need to do the class anymore.
It sounds to me like the DMV took action against your license, even though a criminal case was never filed against you. If a criminal case was never filed, there were likely problems with the case, but the DMV normally doesn't concern itself with such details (unless you request a hearing). The benefit of having retained an attorney then was to have hopefully have won your DMV hearing--that would have given you full driving privilieges without having to jump through hoops now 15 years later. Unfortunately, if the DMV did take action against your license 15 years ago, the DMV will likely now require that you complete the 18-month alcohol school and meet some other requirements as well. You should check with the Mandatory Unit to be sure (916) 657-6525, but I suspect you will be told that your license will remain suspended until you complete the 18-month alcohol classes.
You can get a copy of your DMV printout at local DMV. If it is there on your record, you would have to get a referral from DMV to take the multiple offender program and would be ineligible for a license until you finish the course without eligibility for a restricted license. Good Luck
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