Are you sure or do you have question at times too

I have received my 9 submission coins 2008 Silver Eagle Proofs back from NGC. Of my submission I received 3 PF70 and 6 PF69. I have reviewed the grading and have found that NGC has under graded 3 of the coins. 3 of the 2008 silver eagles disserved the grade of PF69 and 3 were under graded to PF69. I am not happy with the grades. I am going to resubmit these 3 coins back to NGC for a second look. If they fail to upgrade then off to PCGS they go. I just wonder about these coins and how NGC grades them. They receive 60,000 or so of these coins in the first 21 working days in Jan. NGC must grade 2850 or so Silver Eagle coins a day. With numbers like this does your coin get a long look? Makes you think, 2850 a day is 356 silver eagle coins and hour. I have talked too many; some believe that mistake happen in the grading process. So how true is the grade on modern coins fresh from the mint? I am just asking the questions. I think this grading thing is not crack up to what you or I may think it is. My comments of only for new coin obtained directly from the US Mint.