A 10 (eight digit number was produced in 2005 and 2006. I have actually started to see a few 11's for fall season bags.
So for 2006 You would see holograms with 8 numbers
10XXXXXXXX and 11XXXXXXXX
2005 - 7 numbers if its a nine
9XXXXXX and 10XXXXXX
2004 (7 numbers)
8XXXXXX and 7XXXXXXX
etc, etc.... I think this is a pretty good method, until you get around the 2's and 3' and 4's. The first hologram started with a 0 (7 digit) number. The older chanel numbers are a little more tricky, because by the time the hologram had a 2 the bag was probably from the late 80's early 90's.