To be clear, I am, in many if not most cases, an advocate for acceleration for learners of high cognitive ability. (Not surprisingly, when the life outcomes related to acceleration for myself, many members of my family in my generation, and in my children's generation have been notably positive on balance.)
However, advocacy should be based on sound evidence, and also tends to be most effective when it communicates in a language comprehensible to the decision-makers. So while Gross' case studies (as well as Benbow's similar studies using the out-of-level SAT as a proxy for cognition) provide evidentiary support for acceleration based on cognition as a general approach, they don't necessarily work when attempting to convince current decision-makers that cognitive assessments based on a completely different design establish a need for acceleration to a specific academic level. I am not saying that this is necessarily a justifiable response, simply that it is a frequent and not unnatural response.
For my own part, I think the data are clear that acceleration as a strategy is more effective than not for HG+ learners (at the group level; obviously, individual outcomes will vary), but I do not think the data are nearly as clear that specific academic placement decisions (e.g., math or reading level) can be made based purely on cognition. Many factors besides cognition affect academic achievement and classroom performance, including the presence/absence of other exceptionalities, executive functions, social skills, other soft skills. In a more-or-less traditional school setting, these factors have to be considered in placement decisions. If, of course, an educational setting allows for fully scaffolding the other factors, then one can advance more purely based on what turns out to be cognition. (Viz, homeschooling.)
And another technical note: although it became extensively associated with GT research through Terman himself and subsequent researchers, the SBLM was not designed for GT populations either (consider that Terman designed the scale with the assumption that cognitive development tops out at age sixteen, and Binet, of course, originally designed it for the other tail, to demonstrate that intellectually impaired children were educable). It's not really superior to contemporary instruments in design--just different.
And yet another note: the SBLM specifically may, for some educators, trigger some negative impressions, due to Terman's views on eugenics, gender identification, and gender roles, which generally conformed to those of the era in which he lived.
