call for expertise!

i spend lots of time in my car. and i mean lots. my office is a bit away with traffic, my friends in the city are farther, and i'm a busy girl. this is okay, because:

1. i like my car. it feels like a tiny airplane.
2. when i'm driving, i'm generally headed to out to see people i enjoy.

that being said, i've developed a habit. not only am i generally wiggling around and singing while killing time in traffic, but i'm also checking license plates. strangely, the people i love generally drive one of the following cars:

-jeep grand cherokee (traditional)
-volkswagen passat
-saab 9-3
-ford explorer (traditional)
-subaru (the boob)

almost without exception, the cars in question are either black or silver. thus, i'm constantly checking these cars as i pass them on the road. as a result, i've become really familiar with the consistencies among license plates on different types of vehicles. there was a point where i was memorizing as a i drove along without really thinking about it and could reiterate the license plates of the last ten volkswagens i'd passed, but i was developing headaches and killed that habit pretty quickly. being a visual learner, i don't see the numbers as much as the patterns of the numbers, and now i'm wondering why this happens?

for example:

-on a saab in massachusetts, it's pretty common to see something like 13(#)(#) Y (C or D).
-on a ford explorer made in the mid nineties (the boxier ones), the tags frequently read 4(combination of 5,6,7,8 in the next three slots) JD.

i've heard that license plates are made sequentially, but do dealerships issue requests for license plates in clusters? does anyone know?