Convictions and endorsements serve different purposes.
A drink driver's licence is endorsed for 11 years because there are additional penalties for re-offending within a period of 10 years. The court must impose a minimum three-year disqualification if there is a repeat drink-drive offence in that period. The endorsement allows a court to see easily when this rule applies. The endorsement remains for an extra year to allow for cases where the new offence was within 10 years, but the case only comes to court in the next year. Drink-drivers who re-offend within ten years also have to have a medical assessment before recovering their licence.