Blocks and Spirals can always lead to this kind of "hidden slippage". For example, the Marines were originally scheduled to reach IOC with Block 2 in 2010, so by that count they are "only" five years late. But at that time Block 1 was supposed to have "warfighter utility" with weapons qualified and Block 2 was a step beyond that; today's Block 2B/3I has envelope limits (40 kft and Mach 1.2/5.5 g for the B model) and no external weapons.