I am not familiar with the JSAIS or SSAIS, not being in SA...

I did do some poking around, though, and found some small studies that found pretty noticeable ceiling effects even in unselected populations of 6 yos, so, yes, I'd be pretty concerned about the ceiling. Couldn't find any sign of extended norms for the JSAIS.

The WIAT ceiling effects probably had to do with the item sets, which are lockstep by age/grade.

...pronounced like the long vowel and first letter of the alphabet...