I would think the last defect is what you have going on with your 7 right now. Is the first time requesting an exchange for the 7? How many 6 units did you go for till you found one defect free?
I have been reading your replies and laughing my head off. I have always seen threads from @Alexrat1996 and never realized he has extreme OCD with iPhones. And I'm not picking on him, just making A direct observation. But I realized how Many times I responded to his threads with concerns like this, until you pointed out how concerned he always is.
At least he is always respectful from what I have seen. But his threads are entertaining. I hope he finds a happy median. But unlikely for him as it appears.
So many children in this thread name calling the original poster. If his screen has some dust or other problem, that doesn't make your iPhone less special. Stop blaming the user.