Even though you have written down the history, you have to link it to the key. If you get hit by a truck, the story and the key are separated. On this tag summarize what you know about the history of this key. Use two tags if you have to. If it is a less well known key, add the maker and date of manufacturer also.
String tags are available at office supply stores.
Besides preserving the stories for posterity, documented keys add a lot of interest to your collection. Visitors like to hear stories concerning keys. One interesting story begets another. Tell a few and you are likely to get one in return.