Well, zip codes were a new system back in 1963. The United States Postal System developed zip codes as a method to provide increased efficiency and organization to mail handling.
The original zip code system as instituted on July 1, 1963 was a five-digit system. The use of zip codes on mail weren't mandatory initially, by 1967 bulk mailers were required to use zip codes.
I was a child when the change came about. It wouldn't have been notable to me except that I wrote letters to my grandparents. The additional numbers didn't make any sense to me at the time, but I did as I was told and added the "mystery" code to the outgoing mail.
Nowadays, putting zip codes on envelopes happens without a second thought. But for those who were already adults in 1963, zip codes were the first of many innovations to come from the 1960s.
In telling my grand kids about the advent of zip code, they look at me quizzically. One of the older grandchildren even asked if I was around when the pony express was active. I seem to recall asking my grandparents the same question.