On rare occasion, I have purchased stamps at different times, perhaps years apart, that had been previously attached from the same sheet.
Such as these. The left hand stamp was purchased at an auction, IIRC Regency.
The right hand was purchased later on
ebay, a few years after I had initially seen it on
ebay (prior to obtaining the left hand stamp) but had not acted quickly enough, though did save a scan. Upon comparing the scans, I noted the similarities of the cancels, and upon receiving that right hand stamp, noted that they fit together like long lost partners.

The following represents a second such story, that time with each stamp accompanied by a copy of the same certificate showing they had until recently been contained within a plate number imprint strip that was sadly broken.

Anyone else with similar stories to share?