Dataflow under the hood information

I don't have links but can say from experience, refreshes are all or nothing. Failure and all entities will be returned to their original state.

Which successful or failed dataflows, you can look in Refresh History and download a .csv for each attempt and see when individual entities start and stop, and if Enhanced Compute Engine is being used.

You should be able to determine from the log too if entities are being refreshed concurrently or consecutively.