A little bird (thanks, Dottie!) forwarded this link to a study that explores scoring "oddities" on the SB-5:
Gifted and Highly Gifted: How do they score on SB-5? A couple of pertinent snippets:
In contrast to the means on the SBS, which seem to be lower than expected, many of the age-equivalent scores appear to be higher than one might expect. The proportion of children that received age-equivalent scores beyond the highest average score for mature adults (19% of gifted students and 40% of highly gifted students) seems implausible even after taking into account documented cautions in interpreting such scores (Sattler, 2001). If these age-equivalent scores are indicative of actual functioning, it seems curious that they are not accompanied by correspondingly high IQ scores. In sum, these scores appeared to be of minimal use in accurately describing levels of giftedness in our sample.
and
Another interesting finding is that some individual's scores varied dramatically between the two intelligence tests (as much as 35 points). Two students in the highly gifted program scored so low on the SB5 that they would not meet intelligence test criteria for giftedness even if the cut-off were lowered to 115. Alternatively, several students who scored at the low end of the IQ cut-off for our gifted program did very well on the SB5 and scored within the range of the study completed by Riverside on child prodigies.