You can use the EDI inventory order staging journal to receive and validate picking list registrations from a 3PL warehouse. The related messages are not included in the EDI tutorial project. So, these need to be custom build during implementation.
If you use staging, you receive a confirmation from the 3PL warehouse that items are picked, with a custom 'XML picking list registration to EDI inventory order' message. This message imports the received confirmation into the EDI inventory order journal. When the import is completed, the applicable validations are done automatically.