So I got that itch again this morning, and actually managed to dig up enough information that I could tease out the full rules for Apple's new serial number format

# 11 digit:
# 0-1 = plant code
# 2 = year of manufacture
# 3-4 = week of manufacture
# 5-7 = unique unit code
# 8-10 = model code

# year is last digit. repeats every 10 years, "4" could be 1994 or 2004 etc
# week is two digits, 00 through 51, week of year

# 12 digit:
# 0-2 = plant code
# 3 = year of manufacture
# 4 = week of manufacture
# 5-7 = unique unit code
# 8-11 = model code

# apple is using a "base-27" numbering system for year and week, the digits are: 123456789CDFGHJKLMNPQRTVWX
# the number notably does not include vowels AEIOU, and consonants BSYZ
# the year starts in early 2005 with 0, 1 is late 2005, 2 is early 2006, M is early 2014, etc
# the week code is the number of weeks offset from the year. (either starting with the first or 28th week)
# 0123456789CDFGHJKLMNPQRTVWX are weeks 1-27 and weeks 28-54
# (all years have 52 weeks plus one or two days, so the system must be able to handle 54 weeks)
# how apple interprets years when it hits 2018 is unclear. X is early 2018 but is 0 or Y late 2018?
# or will X be skipped and 0 be used for early 2018?

(before the change, 11 digit numbers were computer serials, 12 digit were service part serials, now 12 is computer, and iirc 17 or 18 are part)

As my notes indicate, I don't know what will happen in 2018. Apple needed to have at least a base-27 (not base-26) number system for this to work, because there are more than just 52 weeks per year. Since they exclude vowels and BSZ for robustness, they could go through to y (unless counting it as a vowel I suppose) though only needing to apply it to the year component, but no one seems to know for sure. If we stick with 27 and not 28, then when it wraps, 0 won't represent early year, it will represent late year, which also doesn't look too clean, possibly suggesting X will also be skipped when it wraps.

So what do you think they have in mind?

(this is kinda unfortunate, as it makes it a lot more complicated to figure out the manufacture date by eyeballing the serial number, I will miss that)
_________________________
I work for the Department of Redundancy Department