I have noticed that the data shown in the dynamic reports does not match with the actual numbers. Transactional messages are like custom resource and not a delivery resource otherwise you could find out the delivered/ processed count from delivery dashboard itself. There could be two ways to find out the kpis for transactional messages:
1. Go to your event configuration in ACS and click on "Latest Transactional Events" under the summary on left. This defaults to maximum 25 records (and the count is not coming always under count element in json response) so you can manipulate the URL to get just the count.
Actual endpoint: https://<ACS endpoint>/rest/head/<your EVT Id>.json?_order=created%20desc&__securitytoken=<security token value>
Altered endpoint to get the count: https://<ACS endpoint>/rest/head/<your EVT Id>//_count?__securitytoken=<security token value> This gives the number of transactional messages sent for that event
2. Another way could be to create a workflow with a query. In properties, select the resource as your EVT name/ ID. You can filter on Real Time Events > Created or Status fields. Here you would be able to preview the count based on Status(Sent, Pending, Pending Delivery, Delivery Error) or capture the count in Advanced tab (new element). If the purpose is just to validate the numbers, it can be done with the preview itself but in case you need to get a report then you can use Extract File activity in the workflow.