I hope you are able to find some more useful responses from your local educational authorities.
An interpretive note: in my experience, it is not uncommon for learners with strengths in language and relative weaknesses in visual-spatial/perceptual areas (sometimes classified as NVLD) to struggle with reading early on, when it is more of a mechanical, and even visual-spatial skill, but then suddenly take off with reading once they (finally) make the transition from learning to read to reading to learn, and it becomes primarily a meaningful language task. That would, btw, make the decline in verbal cognition scores more easily understood, since he had limited access to high-level text all the way through middle school.
On the flip side, many of these students also seem to get by in mathematics as long as it is arithmetic-based--the "vocabulary" or basic language of math--and everyday-contextualized. Once they hit higher level math (usually in middle school or high school--sometimes not until university for some very high cognitive learners), the underlying visual-spatial weakness appears to interfere with more abstract math. Note, by the way, that his one high score on the 2013 WISC-IV PRI was in Picture Concepts--which uses concrete-familiar images, thus making it more amenable to verbal mediation/compensatory strategies. IOW, why that score is in the same range as his VCI subtests.
A related phenomenon I have encountered a few times is that sometimes schools declassify these types of students as LD around the transition into or out of middle school, because they no longer test as LD-reading, and no one thinks to take a closer look at other areas of possible LD, such as writing or mathematics (or they look, but the decision-makers are already kind of mentally locked into reading as the focus). They probably hadn't been writing IEP goals for anything other than reading up until then, and now the student has met or even exceeded the goals, with the next level of goals becoming essentially "make average progress in grade-level curriculum", which doesn't, obviously, need special education (no specialized instruction involved). If they don't take a wider perspective that includes other significant educational goals, they may not see that the LD is still very much there--just presenting in a different way. Every year, (in addition to the students I recommend declassifying because they can handle the curriculum independently) I end up reclassifying a handful of students that were removed from an IEP just one or two years earlier, by their previous school, for exactly this reason.
