Serial & Lot Number Traceability

We purchase serialized components that are used in assembled end-items.  This final assembly is not performed in a 1-to-1 operation; we may assemble a batch of 6 sub-assemblies (using serialized components) and then assemble 2 orders of 3 final assemblies using the 6 sub-assemblies.  We'd like to be able to identify the serial numbers of the various components used in a specific end-item assembly.  This can be done easily with the work orders if the build quantity of the sub-assemblies and assemblies is 1.  It's when the quantity is greater than 1 that we're having problems, resulting in essentially no