Not so much postwar, but a number of secondhand modern-ish pieces did prompt me to think about the past lives of some items I acquired.
AHM: When a friend of mine offered a selection of AHM O scale pieces from a collection his club had purchased, I first hesitated, owing to their funky couplers...until I discovered AHM made conversion couplers that bequeathed 1970's Atlas-style dummy knuckle couplers to them, and found an Ebay seller who had a whole case of them. I bought those cars, and as I researched these pieces, I found that AHM only released about a dozen examples (3-4 each of boxcar, reefer, gondola flatcar and caboose), leading to an effort to fill in the missing gaps. I still don't know anything about the original owner, but I did find a Korvette's price sticker on one of the boxes.
Assorted MTH warehouse auction pieces: Some cars with original boxes had price stickers from dealers, at least one of which was still in business.
A pair of MTH Chessie 50' boxcars I purchased from the collection of a friend-of-a-friend who was selling off his collecion following the decommissioning of his layout owing to age. I wondered for a time whether I should change the source of the cars in my records from "collection of" to "estate of" when I found out a few months later that the gent had passed away.
The dozen K-Line aluminum tankers I got from another Cabin Fever auction I pictured in a recent 'Buy Anything Cool' post included some examples bearing inventory number stickers.
That one piece whose former owner I do know came from a friend who passed away (you may know him as the voice of most MTH subways) on Veterans Day 2019 after a relatively short battle with a trio of brain tumors discovered only in March of that same year. The only items I was able to buy from his collection were a MTH Premier NKP 765 and some Bowser RoadRailers. Not long after I and another friend of his had started on an effort to inventory his collection, we received word from his wife that she managed to find a dealer willing to take the whole collection in one shot, so on short notice I was able to gather enough cash to purchase the 765 and some Roadrailers the night before the entire collection was packed up and hauled off. Before taking possession of the loco I managed to figure out how his layout power was controlled, and got enough of a stretch of clean track to have this loco put in a star performance before it went home with me, the last locomotive to operate on the layout before it was dismantled.
As I slowly inventory my own collection, I have been including notes in the records detailing the circumstances of acquisition when they are known, and any modifications/ repairs/ upgrades I may have made. I've thought of inserting notes in the boxes of some pieces I have more or less complete acquisition info for (or even a QR code linking to YouTube videos of mine where that item appeared), that may provide a point of curiosity to some purchaser in the distant future in the event my collection has to be liquidated without my being around to see it off.
---PCJ