The filler metals manufactured to AWS/ASME filler metal specifications are identified by the label on the outside of the container. The label is the manufacturer’s certification the filler metal meets the applicable requirements of the AWS or ASME filler metal specification.
If the purchaser requires something more definitive, the purchase order must specify what supporting documentation and what level of testing by the manufacturer is required.
I suggest you obtain a copy of AWS A5.01 Procurement Guide for Filler Metals from AWS or ASME. It will tell you what information must be provided in your purchase order to get the documentation you need.
Best regards - Al