On 1 November, Stanley Gibbons Auctions sold "The Cyriax Collection of Great Britain." I entered the winning bid for a Penny Black. On 10 November, I received a request from PostNL's customs-clearance department to pay 9% import duty on the item, plus € 12 service fee. I paid it the very same day. On 16 November, PostNL informed me they had received the item from their own customs clearance office.
On 17 November, the track-and-trace app informed me the mail had been sorted, sent out on delivery, and dropped in my mailbox within 2:30 hours. This is a highly suspect timeline. PostNL also has an app that shows the mail they will deliver. The app shows a picture of the mail item with expected date of delivery. Originally, it showed 17 November. Yesterday, however, it showed 21 November as expected delivery date, disproving the information shown in the track-and-trace app. The picture showed a white envelope with a combined address and customs-declaration label at the front.
Upon returning home from holiday, I did not encounter the mail item. I contacted PostNL. Of course, they told me the item had been delivered on 17 November. When I returned home in the late afternoon, I found a large envelope rammed into my mailbox. The package did not fit the aperture and brute force was used to stuff it into my mailbox. It took me a few minutes to dislodge it. This was a brown envelope with an address label at the front and a customs-declaration label at the back.
You, already, may have guessed: it was the missing auction lot. Apparently, some incompetent postal worker just pushed a couple of buttons showing the item as delivered and threw the item into the return postbag for the UK. Either Stanley Gibbons, or Royal Mail repackaged it and sent it back again.
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As for the lot: it is a Penny Black from plate 6, lettered 'AC', i.e., from the top row of the sheet. What is interesting about the stamp is the cancellation. The stamp was cancelled by a 'Maltese Cross' in
ruby ink. This ink colour has been identified as unique to Aberdeen, Scotland.