From the Lawrence Daily Journal-World for Aug. 6, 1975:

The U.S. Postal Service announced this week a change in postmark policy. By the end of the year the names of cities, which had been removed five years earlier, would be put back on the postmark; however, it could be that the name on the mark might not be the city in which the letter was mailed. In 1970 the Postal Service had begun marking first-class letters at 250 centrally located mail processing centers instead of at local post offices. At that time, the names of cities were dropped from postmarks and replaced with center zip codes and state abbreviations. Lawrence mail, for example, was now shipped to Kansas City for marking. The Lawrence post office had not made the transition to the mail processing center until 1974, but local patrons still had the option of getting a Lawrence postmark.