@RiotDemon Thank you for posting that; it has been a while since I read the history. I had read similar before (back when microsoft released windows XP there were articles about how that was Bill Gates thinking he was the second coming, and ‘related’ stories noting that ‘XP’ and even ‘X’ was used to represent Christ as an abbreviation historically.
When I worked at the auto parts store in high school/college we managed to get on an advertising trade journal’s mailing list and got subscribed. There was an article and a followup based on reader mails (before email!) that covered using ‘XMas’ in advertising; it had been used back to the 1920s but rarely; it came into more common use in the 1960s to early '70s. Distressingly I cannot find the articles anywhere online. There was mention of GE using ‘XMas’ in an ad for holiday lighting back in the '20s and switching back to Christmas or holiday due to complaints received (and again I can’t find this reference online).
Per this article and followup, the abbreviation was best to be used for ads that wanted separation from the religious/sacred aspects of the day, and were aimed strictly at the ‘sale’ or ‘gift’ or ‘commercial’ aspects and to try to spread the appeal of the ad to the then not large but growing segment of the population that didn’t include Christmas in their religion or would be turned off (heh, '70s) by a reference to Jesus or Christ.
‘XMas’ was literally promoted as the way to do Christmas advertising while removing the implied religious aspects of the day from the ad. And there was pushback even then, leading to the followup article that included the GE Holiday light reference.
Your linked article is correct, and I had forgotten that usage of XP and X in old scripts/texts, presumably as space saving did exist so the was not made up for advertising. Thank you. But I think that trade journal was correct in that its modern use in advertising is primarily for the other purpose, not just ‘carrying on use of a traditional abbreviation’.