For file names in our Book trade correspondence project we use yyyymmdd
with an author prefix and if necessary a sequence suffix for each
letter. Are there any standard practices for non-dated letters, or
letters with incomplete dates (only the year, only the month, etc.)?
Neither Google nor a (superficial) trawl through the most likely
projects using the TEI brought up anything.
I'd be very thankful for pointers.
Adriaan van der Weel
Book Studies, University of Leiden