Jibberjabber, a previous contributor to the Tapatalk Zodiac forum, forwarded me a newspaper article from the Sacramento Bee published shortly after the disappearance of Donna Lass, on September 24th 1970. This newspaper article, highlighted by Jibberjabber, had all the ingredients to create the 1974 Christmas card mailed to Mary Pilker, including her address.
If the Sacramento Bee (or another contemporary article containing this information) was the source of the inspiration for the 1974 Christmas card, would this lend credence to the Mary Pilker communication being mailed by the Zodiac Killer, irrespective of whether he had a hand in the disappearance of Donna Lass? We know the Zodiac Killer was able to source newspaper articles from distant years, so does the similarity in wording between the 1970 Sacramento Bee article and 1974 Christmas card, specific to the religious tendencies of Donna Lass, lean towards the Zodiac Killer being the author of this festive message to Mary Pilker in South Dakota. Thanks to Jibberjabber.