MacRumors posted an article back in 2010 with a partial explanation of the 12-digit serial number format, at least the general structure and how to decode the date. Apple legal asked MacRumors to remove the article and they complied, but there were reposted copies around.
Based on that article, your list of characters is almost right, but there are slightly different lists for the half-year and week.
The half-year list starts with C for the first half of 2010, and goes up to Z for the second half of 2019, skipping vowels, thus "CDFGHJKLMNPQRSTVWXYZ".
The week list starts with 1 for week 1 in the half-year and goes up to Y for week 27, skipping vowels, B and S, thus "123456789CDFGHJKLMNPQRTVWXY".
It appears vowels were skipped as an arbitrary choice, but B and S were skipped in the week list because of potential for visual confusion with 8 and 5 in that position. It was not necessary to skip S in the half-year list because 5 is not used there.
For 2020 and later, Apple will probably change the serial number format again, most likely extending it at least one more character. Then we start all over again trying to decode them.
