the week codes only require
0123456789CDFGHJKLMNPQRSTUV
normally it'd be only 26 characters (not 27) since they need to cover the weeks in the first or last half of the year, but leap years have one more week (with one day in it) so they extended the list to 27 characters. the last day in the leap year is coded as latter half of the year, week 27.

I'm pretty sure they removed I and O to avoid confusion also with 1 and 0, not just because they are vowels. Considering how hard it's getting to read them and how they all have barcodes on them now, apple may just do away with that and "reuse" those previously shunned characters if they run out of address space before they change formats again.


I work for the Department of Redundancy Department