Old North Church 1723-1973 Postal Issue Heritage Series 01

I cannot seem to find any information regarding this particular piece and the envelope. I do know about the history of the Old North Church, just not the content and envelope. I wondered about this being printed on USPS paper, and postmarked/cancelled (probably for for collectors), for the 250th Anniversary, yet the stamp is a 1971 issue, so this would not be a first day cover. The postmark is Boston, Mass. April 15, 1973.

Thank you for any opinions, suggestions, and comments about this one. I am enjoying seeing everything posted here, and learning more about what we're looking at, and the history behind it. This is a double bonus, as it is about history, on top of being history.

This would be considered an "event" cover. Event covers often have stamps that seem to have little to do with the event being commemorated. Here at least it was a stamp that is somewhat, if not directly, related. It is usually the postmark that is the important philatelic detail on such covers.

I found the answer for you:

Were there ever any other events commemorated in this series? After some brief searching, I could not find any.

Thank you both very much. I hadn't looked under the word 'cachet' which is new to my vocabulary. I very much appreciate you finding those articles, and the time you, and blcjr, took in sharing information.