I am having trouble identifying a Date Code on an IC chip.
Hopefully someone out there can help as I'm not sure where to look.

If you can definitively solve my problem (discussed below), then great!
But if you don't know where to start, I'd accept your work as an
answer if you look up the datecode formats of at least 10 major
companies that produce microcontrollers (whether you find a match or
not.)

--------------
Here's more details than you probably need to know:

I have an integrated circuit chip with the following label on it:
DUNCAN
8517B2

The part is a microcontroller with ROM/RAM/EEPROM on it and was in a
product made by Duncan Industries.  Since it has ROM on it, it must
have been custom ordered by Duncan.

The Duncan website mentions:
"In mid 1996 the microcontroller in the product was switched from a
Sanyo microcontroller to a Motorola one."  The product was bought in
2005 so I assume this is a Motorola chip (unless they changed brands
again).

I called Motorola/Freescale technical support and asked who assigns
the datacode on a custom ordered part, Motorola/Freescale or the
company ordering the part.  They said Motorola/Freescale and said the
datecode meant the part was manufactured in the 17th week of 1985.

This is clearly wrong as:
1] the product wasn't even manufactured back then
2] I depackaged the chip and found that the minimum feature size is
about 0.6 microns.  This was not possible back in 1985, as shown here:
fig 5 - http://www.electronics-cooling.com/html/2000_jan_a2.html
fig 4 - http://cnx.rice.edu/content/m1032/latest/
(But it looks feasible for 1996 or later, which matches what Duncan suggests.)

So what I want is the following:
1] If you think this is something else (not a datecode), let me know
and why.  If you don't feel qualified to answer this, and don't feel
like it, feel free to skip this part.
2] Try to find a manufacturer of microcontrollers who's datacode
format not only fits the "four numbers - a letter - then a number"
layout, but also makes sense (ie manufactured 1995 or later).  I'd
like you to find the date code format of at least 10 major companies
that produce microcontrollers.  If you don't find a match after this,
I'll still gladly accept your hard work as an answer.

Thank you.