The Pocket Museum is a great mail art work if you are an archivist. It contains more than a hundred artists, but it isn’t very big, because every contribution can fit in a pocket obviously (see Everybody has a museum in their pocket and A receipt for nothing).
But nothing is clear cut when dealing with mail art. There is a lot of unidentified objects in the Pocket Museum; pictures, collages, drawings and small objects that have travelled from an unknown artist’s pocket to this tiny museum.
The problems concerning Pocket Museum is part of an overall problem you encounter when trying to categorize a messy mail art archive. There is too much information and not enough: Every time you open an envelope or a file in the filing cabinet it tumbles out with small pieces of paper or objects, and many other art works are missing important pieces, that are probably in boxes and archives somewhere else in the world. A map of the archive is going to have a lot of uncovered terrain and many dead links, but also links, that connects the archive to other mail art archives. Even with a good map you will still get lost in the archive, and perhaps that is okay.