Hi eveline8,
BroadLog ID is the field/Schema which is actually responsible for identifying Delivery success to Recipients.
If the recipient is being targeted multiple times for same Delivery, there is no out of the box field (corresponding to Deliveries) which could identify the specific 'Send' of that Delivery leading to an Open/Click.
Even a comparison of Event Date (within Sending Logs) with approximate time of API Calls won't give a fair idea as to which API Call is responsible for the Open/Click.
No User Session (end-recipient identification) values would match with any detail of API Call as well.