How to know the build date from retail box?

I am going to buy nexus 6p on friday :laugh: . My previous phone was Lg g4 which died after 7 months of use :( because of a loose connector in the motherboard. Basically it was a defective unit. My phone serial number was S/N: 505 which was the earlier produced unit. [505= 2015 May, 506=2015 June, 506=2015 July.... & so on} So this time i wants to buy a later produced 6p. But how do i know the build date without opening the box?
I am posting a sample picture of the 6p retail box [collected]:



p.s: does the frost white version gets dirty easily? I mean all white :D :laugh:

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