HP serial numbers

[PeterG]

On HP 15Cs made in the USA serial numbers appear on the top edge in the form yywwAnnnnn where the number yy + 60 denotes the year; ww denotes the week produced; A, the USA (B for Brasil) and nnnnn the sequential number of the calculator produced in that particular week.

Consider the following serial numbers of HP 15C calculators:

2505A79855 on Ebay
2638A19369 on Ebay
2707A54723 on Wikipedia
2350B38564 on Ebay
And my two:
2249A0994 and 2413A45059
And from Brasil 2350B38564, on Ebay.

Although the sample is small we can deduce from calculator number 79,855 that at least 80,000 were produced a week in the USA in 1985. 80,000 a week for 50 weeks a year for 7 years (1982 to 1989) is 28 million with an additional 14 million or more from Brazil (assuming 40,000 per week given the Brazilian serial number 38,564) giving an estimated total of 42 million.

This seems to me to be an implausible number even without considering the other models that HP was producing at the same time. Could it be that the nnnnn component of the 15C serial number is not the number produced in a week but rather the sequential number produced in the year?