Got it...thanks. In that case, each row of the query will have a row in the notification table - 12 rows added to the notification table. So from there it works as I said, it just runs through the table in FIFO order using however many threads based on your number of CPUs. How many of those reports would be processing together depends on the order of the rows in the notification table  - such as were there other rows inserted before those subscriptions. If these are long running, the reports that are fired off after these 12 would likely be waiting. That's why you can often see the bottlenecks in the notification table - there are only so many threads to process the reports so those would wait until the threads are available to get picked up for processing.
Not sure if this link helps in understanding it better but take a look at this blog post on subscription processing:
SSRS Subscriptions (What goes on "under the hood")

Sue