OK--there are three models of the ImageWriter II, and this should help...
Any "fog" colored ImageWriter II (which is the Apple IIc color and lacks the words "ImageWriter II" on the cover) was made sometime between late 1985 and early 1987. There isn't a clear-cut code to the serial numbers on these.
The same is true of the first generation platinum model. Here is an example:
http://www.ebay.com/itm/Apple-Image-Writer-II-vintage-NO-2-/231213156134?hash=item35d560c726:g:7noAAOxyeZNTWWa0
The key differences for spotting one besides the serial number are the weight (heavier) and the location of the ports. The newer, lighter weight ImageWriter II/L is the same color but the ports are in a different spot:
http://www.ebay.com/itm/Apple-Image-Writer-II-vintage-/231828394887?hash=item35fa0c9387:g
sgAAOSwnLdWqgYm
You won't find as many II/Ls today (they were sold mostly to schools, which explains their abundance 15 years ago and also why the one I linked is the only one I could find on eBay...meanwhile, there's about 20 of the earlier model).
On the II/L, you read the serial number much like you do the old Macs. I can't read the serial number on the one in the photo, so I grabbed my ImageWriter II/L instead.
Its serial number is: TJ1031ZT%C0090LL/A
The "TJ" is the location code. In this case, it's representative of Japan, where the printer was made.
The first digit, the 1, tells you which year this was made. In this case, it is 1991.
The next two digits, the 03, are representative of the week it was made. This was made in the third week of January 1991. Assuming a normal Monday through Friday workweek, it was made any day between January 15 and January 19 of that year.
The "1ZT" is the ID number of that particular unit.
There is a site out there which has a decoder for the nth unit made that week. It doesn't accept the % sign, so I deleted it and it seemed to work fine. Basically, it converts the code into a digit.
http://macfaq.org/serial.html
My ImageWriter II was the 2305th made that week.
That number may seem high (although selling 2305 ImageWriter IIs could have been possible back then), but Apple does seem to spit out large quantities of particular models at any given time, presumably when inventory is getting low or something new is coming out. This was probably done to ramp up II/L production. I have noticed a lot of Mac Classics concentrated around November 1990 and June 1991 (the latter was probably to fill school orders). SE SuperDrives were made most often in January 1991.
These things did sit around for a while sometimes. My LC, which I got new in March 1992, has an October 1991 date (so does its monitor). My iBook has a February 2000 date; I got it in August of that year. (It was one of the very first 64MB models). Both were purchased at mom-and-pop Apple dealers. Even my MacBook Air, which I bought last March, had a November 2014 manufacture date.
