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Did they give you any information about index or subtest scores? Or just an FSIQ? One of the differences between the WJIII, WRIT, and WISC-V is the extent of timed hands-on subtests. If your DD performs significantly different on timed/untimed tasks, that may be enough to affect the global score.
I would start by requesting full test results, including subtest and index scores (and preferably raw scores, too, if you can get them). (It sounds like they are in process.)
Keep in mind, though, that 5 yo scores are not as stable as 8 yo scores. Also, the WRIT and WJIII were both over 10 years old at the time they were administered, which means a certain amount of score inflation would have been expected, so a little bit of the decline in scores may be due to corrections going from obsolete norms to updated norms.
