For the past few years at Duke, we've been appending additions (new accessions) to the end of existing finding aids when those additions are unprocessed or minimally processed. Here is a link to a somewhat exaggerated example with multiple accessions: http://library.duke.edu/digitalcollections/rbmscl/bingham/inv/
The hope is to consolidate description for each collection into a single finding aid. You'll notice that some of the accessions have box lists, while others do not. We record a brief scope/content note for each accession as an additional 520 field in the collection's MARC record. With some exceptions, accessioned material is available for patron use regardless of its processing state. All accessioned boxes are barcoded and linked to the collection's catalog record.
Currently, our finding aids are generated in an XML editor with a series of templates rather than a database.