An over-run is when you order 500 plastic credit cards cases and you receive 515. An under-run occurs when you order 144 coffee mugs but receive only 140. Manufacturers would rather have a slight over-run than an under-run in case you need exactly 500 cases for a conference. As with any printing process extras are printed just in case some items did not print correctly. Call this a safety margin for your benefit. Only a few promotional items have over-run. The more expensive an item is the less likely of an over-run. Over-runs usually only occur on high speed, automatic presses.