It looks like Chanel batch numbers go in cycles of one hundred months, with 00xx indicating December 1999, and 99xx March 2008. In April 2008 I assume they started again with 00xx batch numbers, and indeed my latest bottles are in the 00xx to 22xx range, so it looks like the system is still in use. I don't know when this way of numbering bottles came about, but it doesn't appear to be possible to tell the difference between a bottle made in December 1999 and April 2008 using the datecalculator website. I don't know the significance of the remaining digits, but they don't appear to relate to the specific perfumes as I have bottles of Pour Monsieur EdT and No.19 parfum with the serial number 8001. I don't know if any of this is relevant to bottles with five digit serial numbers, which seem to be older.