Yet today zip codes or zip + 4 codes are not required on single piece of first class letter (UPU letter rate) matter. It was not until 1967 that zip codes were require on any mail matter. I quote from a 2018 The United States Specialist
article entitled Transition from Domestic Air Parcel Post to Priority Mail
"Zip code was introduced July 1, 1963 and was an optional addition to your mail. In 1967, inclusion of a zip code in the address became mandatory for bulk mailers of second and third class matter who wished to continue to receive the bulk discount as presorting to zip code was then required. Next zip code became mandatory for parcel post matter as distance zones were determined by the first three digits of the zip code. That occurred sometime prior to 1981. The first record of required zip code for Priority Mail began February 3, 1991 when a discount of 10 cents per piece was offered for mailing of 300 or more qualifying pieces which were presorted by zip code."
So yes that is a nice example of early zip code use Gibby01.
Now to back to the OP's purpose of this thread: