Nice to hear from you again!
There are a couple of different questions here:
1. Should he be retested?
That depends on if there is a reason for it, of course, but that reason doesn't have to be for test accommodations. If he wants retesting to understand himself better (and this is something family resources allow for), then that's a conversation one can have. If the testing is primarily for test accommodations, that runs into question 2:
2. Will testing help to obtain accommodations?
With the SATs currently on deck, then probably not--mainly because, unless you already have one lined up, it is extremely unlikely that you will be able to find an evaluator (either in your local public school district or privately) with availability to test and generate a formal report in time for your school guidance counselor to submit it to College Board for approval prior to the December test date. From what I understand of your region, lead times on private psychs run most optimistically at about 3 months (if they get a cancellation), but more typically about 6-9 months. And turn-around time on the written report is often upwards of a month--or even more. Not to mention response time from College Board (that's actually the quickest part of the process).
And, of course, as you note, the processing speed weakness may not show up this time around. In any case, the previous round was marginal for acceptance by CB for extended time.
It seems to me the decision to update his cognitive testing should rest mainly on other values to retesting (such as his understanding of himself as a learner). And if it so happens that this results in documentation suitable for attempting an accommodation request, -and- that his December test scores don't appear to reflect his actual skills, then maybe an accommodation request becomes a factor. That way, the likely very long lead time on testing results in findings that are meaningful regardless of SAT/ACT/AP needs.
