note what we're guaranteeing about the order

docs/source/interface.rst

@@ -54,6 +54,7 @@ The elements of the list are objects like the one returned by issuing a **GET**
 
 This endpoint allows an external agent to retrieve unused unblinded tokens present in the node's database.
 Unblinded tokens are returned in ascending text sorted order.
+This order matches the order in which tokens will be used by the system.
 This endpoint accepts several query arguments:
 
   * limit: An integer limiting the number of unblinded tokens to retrieve.