Yes, they can pass the screen and still have CAH!  My 2.5 month old CAH daughter passed the MO newborn screen but was diagnosed at 6 weeks.  (Pediatrician asked for re-testing because of enlarged genitalia.) 

Our public health department called to ask if we knew why/how she passed the screen.

Um, no.  Maybe you should talk to an endocrinologist to figure that out...

Jen