Bowed Engineered Flooring Planks

I just purchased 1500 square feet of 7 1/2" wide X 6' Long American Cherry Engineered flooring planks. They have a 1/2" substrate made of several layers and a finished layer made up of 1/4" (american cherry). I opened up the first two cartons and every panel was bowed the long way. On average approximately 1/2" from the end of the panel to the floor. The system is a tongue and groove. The manufacturer claims that this is not an issue?????????? Is this acceptable? Even if it is at a bear minimum the installation has become a lot harder. They claim that the longer the board the more common this is?????? Can someone knowledgable please let me know. I really appreciate your help.