Aren't we talking about 5th letter being Q? So 1,2,3,4,5,6,7,8,9,C,D,F,G,H,J,K,L,M,N,P,Q=21? What am I thinking wrong???
Person said 4th letter is W (=1 half 2018) and 5th letter Q (week 21).
You are simply trying to go easy way and count backwards something that is not supposed to.
You can only count it right the hard way.
Edit: OK, so you obviously noticed that too and edited your post.
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Sorry, you are correct about the date code.
Right. And as a side note W represents the last week of the first half of the year.
Apple doesn't print date codes on their boxes because the S/N already conveys that information.
But they do. Not sure when they began to do that but it can't be very long ago. Even Airpods I recently bought for the present had similar date code printed on the serial number sticker on the box. Those had 12/2018 printed on the label but also serial number matched that, so those did not celebrate their birthday at the factory before shipped out...