http://www.eng.auburn.edu/pub/mail-lists/ssa-managers.Jul96/msg00016.html

let's say the serial number of the part is Ser#: 526M1984 then you  can
figure out the production date like this:   The first digit represents
a year in a decade  -5 stands for 1995-  The second and the third digit
represent a week in this year  -26 stands for 26th week of 1995-  M
stands for first letter of the city where the part was produced
-Milpitas-  1984 is Sun internal and not relevant   So 526M1984 means
the box was manufactured in Milpitas in the 26th  week of 1995.