Hi Martyn,
this sounds like a request for incremental load - which is not natively implemented, but there are a couple of workarounds for it.
Principle here would be to store the data that you've already retrieved either in a "non-refreshable"-query in the query-editor (http://www.thebiccountant.com/2017/01/11/incremental-load-in-powerbi-using-dax-union/) or in an Excel- or csv-file (http://www.thebiccountant.com/2015/12/28/how-to-export-data-from-power-bi-and-power-query/).
You then merge this with your master-table containg all "Review"-values on Left- or Right-Anti in order to return only those values who haven't been passed to the API yet. Then append both tables to get all results in one again.
Or are you looking for sth different?