Hi Martin, Brian, and others,
Apologies for the delay in returning your email. I still don't have my head quite wrapped around Mercurial, but I've managed to upload the relevant stylesheets with changes here:
https://bitbucket.org/CanOfBees/xtf-oai
Please take a look when you have a moment and let me know if you see any utility, significant problems, etc. These changes use the file's date as the OAI dateStamp value. Also, C. Deane (Thanks, C!), made changes to the OAI queryParser stylesheet that allows querying without an explicit $from or $until value.
I don't have an easy fix for the earliestDatestamp parameter (queryParser.xsl, ~line 90), but after indexing with the new PreFilters, I used the bin/indexDump utility to find the earliest datestamp and correct the value.
We done testing here on EAD and TEI XML, so those are the only two PreFilters I've uploaded.
Cheers,
Bridger