18 years ago, I went to the Benjamin Franklin post office at 316 Market Street in Philadelphia and got them to cancel five envelopes with their special cachet on the last year of the previous century / millennium, December 31, 1999. The next day, I went to the window of the post office which was still located at 30th Street in Philadelphia and got them to add a cancellation for the first day of the new century / millennium, January 1, 2000.
One of these double-cancelled envelopes I donated to the then-Atwater Kent Museum, now the Philadelphia History Museum.
