when did state abbreviations change to two letters
List of U.S. state abbreviations Modern two-letter abbreviated codes for the states and territories originated in October 1963, with the issuance of Publication 59: Abbreviations for Use with ZIP Code, three months after the Post Office introduced ZIP codes in July 1963. The purpose, rather than to standardize state abbreviations per se, was to make room in a line of no more than 23 characters for the city, the state, and the ZIP code.[12]
Tax protester statutory arguments Tax protesters argue[citation needed] that there are also no conflicting definitions of "state" or "United States" to this interpretation in Title 26 of the United States Code (the Internal Revenue Code) -- that both of the two times either of these terms are defined as "the 50 states," the terms are localized to the subpart. Under this argument, in those two subparts that define "state" as the 50 states, there is no mention of the District of Columbia or any territories in that definition.