An overhatch, on the other hand, means that more eggs hatched than we predicted. So, if we were expecting to hatch 120 white female Silkies, we might allow 100 to be reserved for orders, planning to use the remaining 20-ish to fill out assortments. But when hatch day comes, if 142 end up hatching instead of 120-ish, that would mean we overhatched.
When that's the case and we hatch more than we predicted, we advertise the overhatch, because there are some chicks available to purchase for last-minute orders. In fact, this is one way you can get a "sold out" breed, by watching for overhatches. So if you've been checking and checking and a breed remains sold out, when there is an overhatch, you do have the opportunity to get some---IF you're able to act last minute.
Unfortunately, we cannot hold these extra "overhatch chicks" from one week to the next, because baby chicks must be shipped right after they've hatched in order to arrive safe and sound.