I'm a parent, not a professional, so take my notes with a big grain of salt
When my 2e ds (DCD, Dysgraphia, Expressive Language Disorder) was diagnosed, I was told (and also read while researching) that any score with a spread greater than 1.5 standard deviations was a potential red flag. When he was tested at school by a school psych, there was no mention of deviations in ability subtest scores being significant, but when tested by a neuropsychologist these deviations were noted and follow-up tests were given to determine what the cause of the deviations might be.
I don't know that there is a different standard for traumatic brain injury vs learning disabilities re the discrepancies in subtest scores; in our ds' case his DCD/etc seems to be related to family history (which we *didn't* know or realize at the time he was tested). When he was tested, his neuropsychologist felt there was a possibility he'd had an early traumatic brain injury.
Hope that helps a bit!
polarbear
