An interesting aspect of this chest of undelivered letters is that it should represent an unprecedented snapshot of ALL the letters from a certain time and place - not just the handful of the ones that survived.
I remember reading about this trove some time ago. It's nice to see that they are progressing with non invasive techniques to discover the contents without the risk of destroying them by opening them. If I ever get back to the Netherlands I will have to visit the museum. Thanks for posting the article.