Thank you very much @Denis_Bozonnet. The bit I don't understand is how I bring into context the ACS ID field in the reconciliation node (this isn't included in our import)? 

I am trying to find a way to split data from an import between reconciled and unreconciled and cannot find a way to do this. I've tried using a Segment and a Split. There don't seem to be any fields when you only consider the incoming data that allow you to do this. For now I've found a work-around ...