The first two digits are the year of introduction. So, when you see a lot of 19's, you can guess when you'll see these products.
The next two digits are the marketing category. For example, to name a few random ones: 25 is track, 26 is O scale rolling stock, 28 is O traditional rolling stock, 29 is operating accessories, 31 is scale steam locomotives, 35 is motorized units, 38 is US made, 42 is Lionscale, etc.
The last 3 numbers are basically sequential numbers which represent different unique road numbers/names.
do you have a complete list?