If we take a look at the three July 31st 1969 letters, you will notice that the communication addressed to the San Francisco Chronicle contained the word "cipher" spelled correctly five times. To the San Francisco Examiner the word "cipher" was spelled correctly three times. In the Vallejo Times-Herald he spelled the word "cipher" correctly once, while spelling it incorrectly on the only other occasion, depositing the letter "Y" into the word (cyipher). The author of the postcard mailed on September 25th 1990 from Oakland, addressed the card as the Celebrity Cypher to the Vallejo Times Herold Vallejo CA. The 1969, 1987 and 1990 communications all used the full address of the newspaper, despite the publicly known July 31st 1969 letters to the Chronicle and Examiner only using the title of Vallejo Times.
But more crucially, both the communications on July 31st 1969 and September 25th 1990 addressed the Vallejo Times-Herald as "Herold", switching the "A" for an "O". I have contacted the editor of the Vallejo Times-Herald for a clearer image of the October 28th 1987 envelope and he promised to have a look in the files. Not only would we be able to view the handwriting in greater clarity, but we would find out if he addressed the envelope "Herold" for a third time. If he did, then the Bay Area murderer would have mailed only three communication to the Vallejo Times-Herald (that we know of), and all would have contained the misspelling of "Herald" to "Herold".
Below is an FBI file from November 8th 1973 carrying the name of Leslie B. Lundblad, analyzing some handwriting in respect to the Vallejo Times-Herald envelope, the Debut of Zodiac letter and the Little List letter. It is accompanied by two excerpts from the Zodiac Killer FBI files (Part One). All three FBI documents feature the address used on the July 31st 1969 Vallejo Times-Herald envelope. All three show that it was addressed to the Vallejo Times Herold, just like the 1990 Celebrity Cypher. What is the betting on the October 28th 1987 envelope containing the word "Herold" as well? Could a casual copycat just keep getting so many things correct, despite having no access to any of the preceding Zodiac envelopes - or is it more likely that the Zodiac Killer was more nuanced than we give him credit for.