I wouldnât be surprised if it fell behind a desk or a piece of machinery and was only discovered when someone renovated the postal facility or finally replaced that 70 year old clunker of a machine.
One thing is for sure, the SFGate article is not going too help with useful information. Lots of words, no explanation from relevant sources at the post office or anywhere else.
Itâs because San Francisco is a magnet for nutty freethinkers who think they can subvert the mail all willy-nilly. The stamps were probably dosed with hallucinogenic drugs. 
You know what this means?
Heâs alive! The Docâs alive! Heâs in the wild west, but heâs alive!
Years ago I worked in a mailroom. One September afternoon we found a couple of plastic mail bins in the grass next to the building. They were full of applications for a nearby universityâapplications that had been mailed the previous year.
I still donât understand why, if he wasnât going to deliver them, the mail carrier didnât just dump them in the trash somewhere. He liked to sit in the Burger King parking lot and drink beer for a couple of hours every afternoon. He could have disposed of them a few at a time.
That Air Force base is now called Joint Base Lewis-McCord, and itâs entirely likely that the holdup was at the base, not with the USPS.
That, and the fact that the yellow stickers were not in use until well after 1945, convince him that the mystery letter has been tucked away somewhere for almost 70 years.
Yes, that and the fact that the yellow sticker is dated â11/15/13ââŚ
Why is 30% of that article about the senderâs love life?
Would you rather that they simply discarded rediscovered old mail, rather than trying to deliver it (and returning it if undeliverable)?
This is a case of a fail-safe system failing safe. Letâs celebrate that, rather than complaining about it!
Have you read How Henry J. Littlefinger Licked the Hippiesâ Scheme to Take Over the Country by Tossing Pot in Postage Stamp Glue by John Keefauver?
I used to have a carrier who would deliver (dump) everyoneâs mail to my box on Monday. I would give the mail to other people, then realized I wasnât being paid as a part time sorter, so I stopped and left them in the box for the next carrier to pick up. I think your boozy mailman might have forgotten where he left the box. Or, you know, maybe he thought youâd deliver them.
No. I thought you were making a joke until I googled it. canât find an electronic copy, though. Keefauver doesnât even have a Wiki page.
At least they didnât return it postage dueâŚIâm surprised that it wasnât stamped âFound in supposedly empty postal equipmentâ Iâve gotten months old mail like that.
He did have a habit of expecting non-postal employees to deliver mail for him. Sometimes when we tried to give him back misdelivered mail heâd say, âI donât want it.â He also had a habit of not delivering the mail at all. When that happened the local post office would tell us âhe didnât feel like itâ.
The sad thing is those were applications for the universityâs nursing school, and by the time we found them the school year had started. I hope the applicants realized that they hadnât really been rejected because no one had seen their applications.
It sounds like you had my old carrier, or his clone. Itâs really funny when written on paper, but so much in reality. Thanks for the laugh. I have no delivery complaints lately, thankfully.
Wait, what? Any links to anything on that?
yeah, I was kinda hoping @daneel would step up here, but I donât think thereâs anything other than links to buy the physical short fiction compilation in which it was published:
All I found so far is this
I knew the name from the hearings on organized crime but little else.
Afraid thatâs all I have. I remember reading it 20 odd years ago in my parentsâ copy of that collection.
I donât recall much beyond the title 
I think Roald Dahlâs Royal Jelly is in there too.
Edit: I checked the contents, that Dahl story is in there. An Asimov, tooâŚ
I remember the one by Richard Matheson - The Distrbutor. That one was creepy.
