The 2.3-16 had to wait a year for intro in the US to meet regs and initial demand was high enough that demand exceed early demand. The 2.5-16 wasn't brought to the US for a few reasons, including the supply and demand issues as the new model came in additional finishes and build capacity at the factory, the price point was near SL territory and the US dealers were more focused on selling the six cylinder 2.6.