"We will have grotesquely unavailable inventory," says one source. Another also expects relatively low shipments, while adding demand could be less than expected thanks to interest in the 5C.
Likewise, U.S. Apple Store sources tell 9to5 Mac the 5C will account for "about 70-80% of new iPhones" available on Friday.
Meanwhile, Apple's Chinese online store, which began taking 5S reservations today, quickly sold out most of its 5S stock. The sell-outs have been taken as a sign of low supply. Apple won't begin taking 5S pre-orders elsewhere until Friday.
Apple remains higher, but has pared its Tuesday gains, which follow a Monday drop that came in the wake of disappointing China Unicom 5S/5C reservation data. iOS 7 launches tomorrow.