No, the GAI can certainly be higher than any of the subtest scores. It has to do with rarity. It is more rare for someone to have very high and VCI and PRI scores, so the composite of the two is higher than either one.
That said, we had a similar experience with dd#2 and the WISC-IV. She was tested at 7.5 on the WISC with an IQ score of 148. Her school was disinclined to believe the score b/c her CogAT wasn't even in the gifted range and her achievement scores were wildly erratic. So we had her tested again on the WISC a year later at 8.5. She also took the SB-V, the RIAS (another IQ test) and the WIAT (achievement) at that time. Her WISC at 8.5 had dropped about 20 pts from the year prior. The psych also told us that it was accurate but I didn't get what seemed like a reasonable explanation for the change other than "fluctuation in abilities." I'm having to assume that time #1 was inaccurately high or time #2 was inaccurately low, but I don't know which it was.
The RIAS score was uninterpretable b/c the spread was so large w/in subtests. Her SB scores w/in subtests also varied from the 16th to the 99th; she was sick when she took it; and the psych had never given that particular test before; she came out somewhere in the upper 1-teens on that one with all of those disparate scores merged into a FSIQ. Finally, her WIAT scores were much higher than would be predicted by any of these IQ scores (2+SDs higher).
I, too, don't know what to make of such wild fluctuations.
As far as your younger son, though, why don't you go ahead and send both reports? Even if the newer one is lacking in detail, it sounds like the scores are qualifying for the school and would only help with getting him in.
