I am not seeing anything obvious that would be wrong in the schema.
I uploaded it and entered in a mutation. It sent back all of the _id's
Are you trying to also link the IDStuff document and the InfoStuff document directly to each other? For that, you would need to “connect” them in a second query, or create them first and then connect them to the Dataset document.
Also, if it wasn’t clear, you do have to request the _id field, just like any other field. I.e. it doesn’t come automatically.