The gov't emission regulations in the 70's were based on parts per million sampling of the exhaust and evaporitive emissions, NOT total emissions per mile driven or passenger mile. Smaller import vehicles did not have to meet the same standards as larger US vehicles. The numbers changed every year, and the companies had to do a 25 thousand mile test of each vehicle configuration to get a preliminary certification including a series of cold start, warm up. hot run, cool down, restart. etc. then a 50 k test to get final approval. Government policies made the goal to get every configeration to pass the 25 k and 50 k tests NOT to have good mileage,and emissions close to the magic number, just get them to pass.Before any tweeking of a product could be done and tested to make improvements the engineers were working to get to the next years numbers.