Hi JitteryCoyote63 ,
upload_artifacts was designed to upload pre made artifacts, which actually covers everything.
With register_artifacts we tried to have something that will constantly log PD artifact, the use case was examples used for training and their order, so we could compare the execution of two different experiments and detect dataset contamination etc.
Not Sure it is actually useful though ...

Retrieving an artifact from a Task is done by:
Task.get_task(task_id='aaa').artifacts['foot'].get()
or if you want the file itself and not the object:
Task.get_task(task_id='aaa').artifacts['foot'].get_local_copy()