At Arizona Archives Online we normalize undated material by taking a best
guess as to its creation.  We often use the birth and death dates of the
creator or a large date span, such as an entire century, for the normalized
dates.  This is based on the idea that while the material is undated, as
archivists, we can take an educated guess about its creation.

So our fields look like:
<unitdate encodinganalog="245$f" type="inclusive"

Hope this helps,

Catalina Oyler
Project Archivist
Arizona Archives Online <>