Overs / Unders
The quantity you receive will be slightly higher or lower than the quantity you order.
Custom manufacturing isn't an exact science. The majority of the time, the quantity shipped and received will be slightly higher or lower than the quantity ordered; this is called overs / unders.
At the time of ordering, overs and unders are expressed as a percentage. Lower quantity orders will typically have a 20% over/under and high quantity orders will typically have a 10% over/under.
Why?
In custom packaging, manufacturers make custom tooling that requires setup time. Thus, each project needs dedicated machine time.
During this setup phase, manufacturers use extra material to test the machines. For example, they check print plates aligned properly, colors match graphics, or die cutter is performing within acceptable tolerance. While testing, rejected products get pulled. More often than not, setup goes smoothly with few rejected products, which results in higher quantity produced. Infrequently, with complicated setup and many test runs, the quantity produced is less than the quantity ordered.
This is common in majority of custom packaging and print manufacturing. Only small runs for paper products, like postcards and brochures, don't have an over / under because it's highly automated and batch processed.