Can I use descriptors for items I buy directly for the job and never stock?
No you cannot. Some light manufacturing systems allow the use of non-inventory parts to bypass receiving and issuing for items purchased directly for jobs. You cannot do anything like this with DBA, which is designed to exclusively use stock items for all workflow processes. Never use descriptors as substitutes for stock items because they are not compatible with manufacturing costing, MRP generation, and job release, all of which are inventory-based.