This strongly suggests that the date code was indeed used at least as early as 1901.
ZIP Code began July 1, 1963, according to The Postal Service History Page.Putting a 20 cent stamp on a private card avoids the one cent card charge." Airmail rates are not shown here; however, it is worth noting that domestic airmail was eliminated as a separate subclass of mail service, effective May 1, 1977.* ZIP 4 was announced in 1978 and implemented October 1, 1983 according to Unicover.ZIP 4 was supposed to make mail delivery faster and hold down costs. (It's called "snail mail" for a reason.) Since nine-digit ZIP codes were introduced, there have been more than a dozen rate increases. Timeline of Significant Dates in Post Office History.On January 10, 1999, however, a one cent charge for the card itself was implemented, in addition to the postage. ZIP is an acronym for Zone Improvement Plan, according to Unicover.