premise: Most zero-coupon CDs are in maturities of six to nine years, and they usually double in value by maturity.  But investors who bought zero-coupon CDs in the secondary market aren't the only ones who may be surprised to learn the full amount of their investments isn't insured. People who paid a premium for standard CDs purchased on the secondary market could also find that those premiums aren't insured if the institutions that issued the CDs failed.
hypothesis: those premiums aren't insured if the institutions that issued the CDs failed