Batch permission creation doesn't create all permissions when InvalidSharingRequest encountered

Google appear to be grouping individual requests to add permissions in a batch as the 400 error message caught by _handle_batch_response() lists multiple email addresses:

Bad Request. User message: "You are trying to invite foo@bar.com, bar@foo.com, baz@gmail.com. As there are no Google accounts associated with these email addresses, you must tick the "Notify people" box to invite these recipients."

It appears that (some) other valid permission creations in this batch are not processed.