Guillaume Courtier has written a Macintosh OS X application that will decode the serial number on your Apple IIGS, IIe Platinum, IIc Plus and Macintosh. The serial number will reveal the date and month, and also where the computer was manufactured.
Requires Macintosh OS X 8.x-10.x 64bit
You can download the app from: http://museepgc.perso.sfr.fr/download/Serial%20Number%20Decoder%201.2.dmg