Some sources suggest that George Dixon might have had 33 title defences but this is imposible to verify.
Roy Jones Junior was 23-1-0 after Tarver I, with his only loss in a title fight being the DQ against Montell Griffin. A good deal of his defenses prior to Ruiz were for unified LHW titles - at the time he stepped up to HW, he held the WBC, WBA, IBF, IBO, WBF, IBA, and NBA titles in the LHW division. After Tarver II, III and Johnson he was 23-4-0, of course.