All of us are human, we can all make mistakes. This goes doubly true for firearm companies.
A friend of mine purchased a Larue rifle on my recommendation. Much to our dismay, it did not function out of the box. (My punishment for highly recommending anything) It was short stroking. Closer inspection showed that one of the socket head hex screws on the boltcarrier key appears crooked. Most likely the head has broken off the bolt shaft allowing the Bolt Carrier Key to become just loose enough to cause the gun to short stroke. Larue Tactical is already replacing the BCG.
If you buy quality, you are less likely to have issues, but there is always the chance of problems. Test your gear.