J
If your data is already stored in folder 'types' (e.g. ProjNo>CentralData>Letters>Incoming>Ext Co Name), I would use 100524-ExtRef-IntRef-toBMOther-Subject. However, if it going to be uploaded to a collaboration tool or Document Management System then the file reference would generally end up as the record number therefore you wouldn't put on any other descriptor other than a controlled number (e.g. could be ProjNo-ContractorNo-DocType-SeqNo). The revision and subject details would be entered into the database separately.
Hope this helps
Hope this helps