The vaccines come in hundreds of varieties, manufactured in thousands of facilities. It is literally impossible to keep them all the same. It's not even possible to keep the ingredients the same. Never mind how they are being mixed together. Even off the same assembly line, the vaccine made on Tuesday is different from the vaccine made on Monday. They speak as if it's all the same. Nothing could be further from the truth. Never mind errors and defects. With top quality controls, the best manufacturing output that can be achieved in mass production is "similar."