I used to manage a "Beowulf cluster" that was actually 80-odd Pentium 4s independently running windows and some specialist actuarial software, each taking a segment of the customer data we needed to model (using a master-slaves type deal). We had plenty of licenses, and helpfully the license check was only done at startup by the Master.
Unhelpfully the licenses were done with hardware dongles and the actuaries (who developed the models and ran local tests to confirm results) needed them too. Over the years, more and more of the dongles had gotten lost (or obsolete - we had a mix of USB and parallel-port dongles) and since the cluster only needed dongles for the "masters" we gave some of them out and slowly reduced the pool of potential master machines. All the ones left were using the older style dongles screwed into the back of the machines.
Then, one day, we had an upgrade, and every machine needed to relicense. Not wanting to get behind the racks, I managed to score a few spare USB dongles someone had hidden in their desk "because it's so hard to find them when we need them", and spent most of a morning plugging them into four machines at a time to do the startup processes.